Children’s stress activation in integrated early childhood special education and its connections to special educational needs and temperament

ABSTRACT

The aim of this study was to examine how children’s stress activation is related to special educational needs (SEN) and temperament in early childhood special education (ECSE). The study had 76 participants from 17 integrated ECSE groups. At the beginning, the children were divided into four status groups as follows: children without SEN, children with language disorders, children with self-regulation difficulties, and children with severe disabilities. The children’s temperament was assessed by their parents. Stress activation was examined by collecting and studying saliva samples from the children on two consecutive days. The results showed no differences between stress activation in the children’s status groups, nor any connections between stress activation and temperament. The high quality of the ECSE groups might explain these results. Further research based on these findings is needed.

KEYWORDS:

• Early childhood special education (ECSE)
• special educational needs (SEN)
• stress activation
• temperament

Introduction

The activation of the stress system is a prerequisite for all learning (Gunnar and Loman 2010, 97–113) Learning is effective when children are able to regulate their stress activation to avoid extreme arousal. In this state, they are able to function optimally and maintain internal balance (Sajaniemi, Suhonen, and Sims 2011, 91–99). The ability to regulate stress develops with the functioning of the slowly maturing frontal lobe (McEwen and Gianaros 2010, 190–222) and this process is fully complete in early adulthood (Romine and Reynolds 2005, 190–201).

In this study framework, stress activation is defined as a biological response that causes feelings of vigilance toward changes in the sensory environment. The feeling of vigilance can be regulated (stress regulation) and increasing self-regulation is part of a person’s executive functions (Chrousos 2009, 374–381; Sajaniemi et al. 2015). The onset of stress activation lies in the area of the brainstem that is also responsible for the regulation of basic organ functions. Stress activation is a direct reaction to stimulus changes, and occurs without conscious consideration. It is controlled by the amygdala, which is activated immediately when the change in the individual’s internal or external sensory environment is experienced sufficiently strongly (Chrousos 2009, 374–381; Sajaniemi et al. 2015). Amygdala activation triggers the HPA-axis (hypothalamic–pituitary–adrenal axis) and the hypothalamus starts to produce a corticotropin-releasing hormone. This stimulates the anterior pituitary to secrete an adrenocorticotropic hormone, which in turn triggers the release of the glucocorticoids, cortisol in humans. Cortisol has an inhibitory function that signals stress activation to shut down. An appropriate amount of cortisol helps maintain homeostasis and provides energy. However, prolonged activation leads to a chronic state, which compromises health (Jessop and Turner-Cobb 2008, 1–14; Nicolson 2008, 37–74; Saxbe 2008, 163–190).

Cortisol can be measured non-invasively from saliva, and this method is extensively used as a biomarker of psychological stress (Gunnar and Quevedo 2007, 145–173; Hellhammer, Wüst, and Kudielka 2009, 163–171; Reunamo et al. 2012, 363–381). Cortisol follows the circadian rhythm. Its highest values are typically at 30 min after awakening. This ‘morning peak’ is followed by a sharp decline, then a more gradual decline throughout the day, ending at the evening nadir (Dettling, Gunnar, and Donzella 1999, 519–536; Sajaniemi, Suhonen et al. 2011, 45–62; Watamura et al. 2004, 125–133). Stress sensitivity varies in individuals and it is regulated by epigenetics and influenced by the social environment. Enriched environments can correct the impact of early adverse stressors (Kudielka, Hellhammer, and Wust 2009, 2–18; Gunnar and Quevedo 2007, 145–173).

Stress activation refreshes the brain and increases intercellular activity. However, prolonged activation of the stress system is exhausting for the brain (Sajaniemi et al. 2015; Gunnar and Vazquez 2015, 533–577; Engel and Gunnar 2019; Watamura et al. 2004, 125–133). Stressors that launch biological stress responses may thus influence learning either by positively challenging the child or jeopardising learning (Rudland, Golding, and Wilkinson 2020, 40–45). There are huge individual differences in reactivity to stressors. These differences are based on the complex chemistry of innate temperament, which is shaped by environmental input (Ellis, Jackson, and Thomas Boyce 2006, 175–212).

Stress influences development and learning, and has therefore been a matter of interest for decades (Baldwin, Baldwin, and Cole 1990, 257–280; Garmezy, Masten, and Tellegen 1984, 97–111; Rudland, Golding, and Wilkinson 2020, 40–45; Bangasser and Shors 2010, 1223–1233; Joëls et al. 2006, 152–158). Stress activation has also been studied in the context of children with special educational needs (SEN). However, the majority of these studies have concerned stress in parents who have children with disabilities (Lovell, Moss, and Wetherell 2012, 682–687; Chen et al. 2015, 9; Dunn et al. 2001, 39–52) and stress activation in children with autism spectrum disorders (Spratt et al. 2012, 75–81; Corbett et al. 2009, 39–49; Corbett et al. 2006, 59–68). These earlier findings indicate that the reactivity of the HPA axis is increased in children with autism spectrum disorders. This has been specifically associated with novel stimuli. Spratt et al. (2012) claim that this is due to difficulty tolerating novel environments and some environmental stressors, which is characteristic of autism spectrum disorders. However, studies of stress activation of other groups of children with special education needs (SEN) are lacking; for example, children with self-regulation difficulties or children with language disorders.

Stress tolerance is highly distinctive. The same kinds of stressors can cause a wide variety of stress experiences. The roots of these differences lie in temperament. For example, some children can cope with difficult experiences without any harmful stress reactions whereas others easily feel overwhelming stress. Due to temperament, children also differ in the intensity of their emotions; in how fearful, frustrated or positively excited they become (Suhonen et al. 2018, 345–358; Bruce, Davis, and Gunnar 2002, 635–650; Gunnar 1994, 175–198; Rothbart and Jones 1998, 479–491; Rueda and Rothbart 2009, 19–31).

In contrast to stress activation, which has seldom been studied among children with SEN, temperament has been widely explored in different SEN groups. Temperamental differences have been found between, for example, children with down syndrome (Gartstein, Marmion, and Swanson 2006, 31–41; Lukowski and Milojevich 2017, 221–232) intellectual disabilities (Boström, Broberg, and Bodin 2011, 1860–1871), autism (Brock et al. 2012, 2271–2284; Korbut et al. 2020, 101492) and attention deficit disorders (Kang and Kwack 2018, 281–285; Karalunas et al. 2019, 236–247).

However, research combining SEN, stress activation and temperament in early childhood special education (ECSE) environments is almost non-existent. Therefore, based on what was presented earlier, it is important to study children’s stress activation in ECSE environments. These environments contain a huge variety of individual needs and temperaments. As a consequence, it is fundamentally important to increase the knowledge about the diversity of stress reactions and to find ways to support the development of all children equally.

It has been argued that different stressors can evoke positive stress, tolerable stress or toxic stress (Franke 2014, 390–402). Positive stress is fundamental for learning and feeling inspired. It promotes resilience and enables individuals to function competently in moderately stressful situations. Positive stress causes minor physiological changes such as an increase in heart rate and a rise in stress hormone levels. Peer relationships, growing learning demands and adjustment to common rules and routines induce stress that remains at a positive level when it is buffered by a responsible, caring adult (Sarada and Ramkumar 2015, 1519–1522). Tolerable stress relates to adverse experiences that are usually short term and manageable (McEwen 2017, 2470547017692328). Such stressors may be, for example, disruptions or accidents in the family. These stressors activate the body’s stress system more intensively but are tolerable when managed correctly through appropriate care from adults. Hence, tolerable stress can be turned into positive stress. However, if support is not available, even tolerable stress can become detrimental. When adverse situations persist for a long period without appropriate support, the state becomes chronic and is defined as toxic stress (Garner 2013, S65-S73; Williams Shanks and Robinson 2013, 154–170; Baldwin, Baldwin, and Cole 1990, 257–280; Branko and Linhares 2018, 89–98). This type of stress can lead to permanent changes in brain development. Therefore, especially in the case of toxic stress, children need sensitive adults, because they do not have the capacity to deal with it on their own (Franke 2014, 390–402). This gradually leads to children’s independent stress regulation and enhanced cognitive functions (Blair 2010, 181–188; Alijoki et al. 2016, 19–36). It also seems that self-regulation skills learned in childhood buffer mental health in later life (Mischel et al. 2010, 252–256). Therefore, these early social relationships play a critical role in protecting the development of the brain. Early childhood education (ECE) professionals and close relatives are a powerful defence against harmful stressors (Gunnar and Quevedo 2007, 145–173).

A significant task of ECSE teachers is ensuring that every child has equal opportunities for optimal development, regardless of their temperamental differences, SEN or home environment (McWayne et al. 2012, 862–878). All temperament traits should be equally acceptable. However, children with different temperaments benefit from different approaches (Rothbart 2011). Therefore, ECE teachers need knowledge on the interplay of temperament, stress activation and behaviour. Temperamentally inhibited children seem to be at particular risk of toxic stress if they lack sensitive care. (Gunnar and Quevedo 2007, 145–173) Children growing in highly stressful environments are continuously operating at the upper limits of their regulatory system (Sajaniemi, Suhonen, and Sims 2011, 91–99). For instance, too many daily activities to choose from might be overloading, especially for children with a sensitive vigilance system. In any case, every child needs adult co-regulation for soothing extreme emotional states. Frequently occurring states of toxic stress jeopardise well-being and learning. The ability to stay regulated in unpleasant conditions is known as resilience. A solid relationship between children and their responsible adults predicts good resilience (Franke 2014, 390–402; Evans and Kim 2013, 43–48). Therefore, focus on strengthening these relationships may help minimise toxic stress responses.

In Finland, children with SEN are largely mainstreamed or placed into integrated special education groups according to the inclusive principles of the Finnish National Curriculum of early childhood education (Suhonen and Nislin 2012). The most important characteristics of inclusive ECSE are appreciation of the natural proportions of children with and without SEN and acceptance of all children regardless of their abilities (Hurley and Horn 2010, 335–350). Children with SEN benefit from rich learning experiences together with their typically developing peers. Consequently, learning through play provides a natural opportunity to interact with others and is an important precondition of inclusion (van Rhijn et al. 2019, 92–112). Being accepted in play builds a positive self-concept for all children and creates a sense of belonging. (Pesonen 2016; Syrjämäki, Pihlaja, and Sajaniemi 2018) The integrated groups in this study were inclusive, in accordance with the group structure, which consists of five children with and seven children without SEN. The groups were most commonly staffed by two ECSE teachers and one nurse.

Tervahartiala et al. (2020) compared children’s stress regulation in Finnish ECE environments and home care. Interestingly, the children had lower cortisol levels during day care than on home care days. This finding contradicts the common assumption that children’s stress tolerance is compromised in noisy group settings with numerous social connections. The explanation might lie in safety-producing ECE routines, scheduled eating and guaranteed recovery time during afternoon naps. These routines might be more tightly controlled in ECE environments than in home environments (Tervahartiala et al. 2020). At best, the ECE environment offers a rich, safe and balanced environment in which every child has the opportunity to thrive, regardless of possible developmental risks.

It is argued that high quality ECE enhances every child’s learning, including those with SEN (Pelatti et al. 2016, 829–849) In a high-quality learning environment, the importance of play and peer interaction is understood, and children have opportunities to learn in their zone of proximal development from more capable peers through play (Bodrova, Germeroth, and Leong 2013, 111–123). High quality means sensitive interactions, recognition of individual needs and strengths, well-designed classrooms, and appropriate pedagogical activities. The most important factors that predict good ECE quality are teacher education and professional competence (Hestenes et al. 2007, 69–84; Pelatti et al. 2016, 829–849; Buysse et al. 1999, 301–314). Secure attachments to teachers also lead to lower cortisol levels in ECE (Dettling et al. 2000, 819–836). It can be assumed that in high-quality groups, children have good opportunities to learn to regulate emotional ups and downs from co-regulative adults.

In the current study, we examined stress activation in children with and without SEN in Finnish integrated ECSE groups. Our previous studies revealed that the children with SEN in the groups in question had problems in self-regulation and concentration and a negative approach towards their environment (Alijoki et al. 2016, 19–36). Children with SEN had a slightly slower learning path in terms of cognitive skills than the children without SEN (Kesäläinen et al. 2019). This might be due to increased stress vulnerability. We were especially interested in the interplay between temperament and stress activation. We also believed that children with SEN might have more extreme behaviour than children without SEN.

Participants

This study is part of a longitudinal study of ECSE by the University of Helsinki, Finland, which has been examining the same integrated ECSE groups since 2012. Data were collected on the quality of the groups, the ECSE professionals, and the learning and development of the children with and without SEN. We followed the ethical guidelines and requested research permission from the municipal authorities and written informed consent from the children’s parents.

The participants were 76 children (42 male and 34 female), of whom 31 had SEN (25 male, 6 female) and 45 had no SEN (17 male, 18 female). The children’s ages varied between 52 and 88 months (M 69 SD 8.5). They were from 17 separate kindergarten groups from the Helsinki metropolitan area. These groups had five children with and seven children without SEN. The personnel consisted of two ECSE teachers and one nurse in every group.

The children were divided into status groups (Table 1) on the basis of their medical records, the teachers’ descriptions of the children’s SEN, and their behaviour in the ECE environment. The categories were formulated by a specialist in clinical neuropsychology, who had extensive experience in both scientific and clinical work. The groups were formed with careful consideration and the overlap between the groups was non-existent in practice. This is explained in more detail in Kesäläinen et al. (2019, 1–17). The status groups consisted of children without SEN (59%), children with language disorders (20%), children with self-regulatory difficulties (13%), and children with severe disabilities (8%).

Table 1. Participants’ status groups.

Children without SEN	Children with language disorders	Children with self-regulatory difficulties	Children with severe disabilities
N = 45	N = 15	N = 10	N = 6
male 17	male 11	male 8	male 6
female 28	female 4	female 2	female 0

Methods

Background information on the children and their families was collected at the beginning of the study. The parents also filled in the Children’s Behaviour Questionnaire in order to provide us with information on their children’s temperaments. For measuring the children’s stress regulation, the ECSE teachers collected saliva samples from them in their ECSE groups in May 2015.

Background information

At the beginning of the study, background information was collected from the children’s parents. The background questionnaire elicited information on family composition, demographic factors, learning difficulties among family members, participation in the children’s birth-related factors, current medications, and developmental concerns. The parents also provided information on their educational level and annual income as indicators of their socio-economic status (SES).

The Children’s Behaviour Questionnaire (CBQ) (Rothbart et al. 2001, 1394–1408) is a widely used tool for assessing temperament in early to middle childhood. We used a form that has been designed to measure temperament among children aged 3–7. The questionnaires were filled in by the children’s parents. The CBQ has 94 items, scored on an eight-point Likert scale from ‘very untrue’ to ‘very true’, and includes an ‘I’m not sure’ response option. The CBQ’s 15 temperament dimensions are: activity level, anger/frustration, approach, attentional focusing, discomfort, soothability/falling reactivity, fear, high intensity pleasure, impulsivity, inhibitory control, low intensity pleasure, perceptual sensitivity, sadness, shyness, and smiling/laughter. These dimensions were further condensed into three main groups using factor analysis: Negative Affectivity, Effortful Control and Extraversion/Surgency.

Saliva samples were taken in May 2015 by the ECE personnel. Most were taken on Tuesday and Wednesday of the same week, as some of the children were absent on Mondays. If a child was ill on the sampling day, the sampling was delayed until they were well again. None of the children took any regular medication that would have affected the saliva samples. We also made sure no one had taken medicine on the sampling day. The children were not allowed to eat or drink for at least 30 min before sampling. The children held cotton wads in their mouths until they were wet. These cotton wads were then placed in Salivate tubes and sent to the laboratory of the Finnish Institute of Occupational Health for salivary cortisol measurement. The first sample was collected in the morning after the morning peak (mean time 9:44 std. 0:27) and the second sample in the afternoon (mean time 14:08 std. 0:18). Unfortunately, due to a lack of resources, we were only able to take two samples per day and were therefore unable to measure the morning peak. However, we were able to examine the decline slope of the cortisol.

Statistical analysis

The data were processed using the IBM SPSS 25 statistical programme. We included all variables identified as potentially significant predictors of cortisol in the analysis. Using the background information, we examined the parents’ education, SES, and the children’s gender, age, experience of kindergarten and sleeping time. In addition, the children’s status groups, overall SEN and temperament dimensions were included as variables of interest.

To examine cortisol decline, the data from both saliva cortisol collection days were combined as mean values. Combining is recommended when examining individual characteristics in relation to cortisol levels (Peters et al. 2011, 1906–1920; Adam and Gunnar 2001, 189–208). The mean of the saliva samples from Day 1 and Day 2 were positively correlated at both time points, morning (r = .611, p < .001) and afternoon (r = .254 p < .05). Cortisol decline was examined using the General Linear Model (GLM) repeated measures and Bonferroni correction by forming cortisol slopes from morning to afternoon.

Temperament dimension consistence was tested using Cronbach’s alpha to examine how strongly the CBQ items correlated among themselves. In this data Cronbach’s alpha values were: Negative Affectivity .315, Surgency Extraversion .431, and Effortful Control .693. For strengthening the reliability of the indicator, we removed the propensity of shyness variable with the lowest alpha (r = .360) from the surgency extraversion, after which Cronbach’s alpha was .721. From Negative affectivity we removed the variable that indicated a drop in excitement because of its low alpha value (r = −.308). After this, the value was .610. We used Analysis of variance (ANOVA) when examining the temperament dimensions differences of the status groups.

Results

Background information

The educational background of the parents was quite high. Of the mothers, 38.3%, and of the fathers, and 31.6% had a university degree or comparable polytechnic degree. Of the mothers, 35%, and of the fathers, 26.3% had a polytechnic or college-level degree. Of the mothers, 16.7%, and of the fathers, 28.1% had attended vocational school. Ten per cent of the mothers and 14% of the fathers had no further education after comprehensive school or general upper secondary school. The annual gross income of the families varied between EUR 20 000 (7.2%) and EUR 80 000 (36.2%).

The children slept eight to twelve hours per night: 59.7% of them usually slept 8–10 h and 40.7% had 10–12 h of sleep per night. Twenty-four children took a nap in ECE day care. Sleeping time during naps varied between 35 min to 2 h, and the mean duration was 1 h 14 min (sd: 0:21).

There were no significant differences between family composition or the socio-economic status of the families with children with SEN and those with children without SEN. In addition, the children’s background information did not correlate with their stress activation. There were significantly more males than females among the children with SEN (25 male, 6 female), thus we did not focus on gender differences in this study.

Stress activation

The children’s stress activation varied on the individual level, but there were no significant differences between the children’s SEN status groups. Table 2 presents the status groups’ means and standard deviations.

Table 2. Status groups’ means and standard deviations (Salivary cortisol nmol).

	Cortisol Day 1 morning	Cortisol Day 1 afternoon	Cortisol Day 2 morning	Cortisol Day 2 afternoon
Children without SEN	Mean 11.20 Sd 6.77	Mean 11.34 Sd 5.73	Mean 11.32 Sd 7.10	Mean 11.90 Sd 5.64
Children with language disorders	Mean11.92 Sd 6.61	Mean 11.32 Sd 8.51	Mean 15.10 Sd 11.12	Mean 8.99 Sd 4.10
Children with self-regulation difficulties	Mean 11.74 Sd 6.77	Mean 10.65 Sd 4.38	Mean 11.22 Sd 8.56	Mean 8.37 Sd 1.60
Children with severe disabilities	Mean 13.00 Sd 7.25	Mean 15.06 Sd 5.67	Mean 17.04 Sd 10.80	Mean 15.17 Sd 8.88

There were no significant differences between the cortisol slopes of the status groups. Figure 1 presents the cortisol declines from morning to afternoon of all the status groups.

Figure 1. Cortisol declines from morning to afternoon of all the status groups.

Temperament

The temperament dimensions of the status groups did not differ. Table 3 presents the means and standard deviations divided by the main temperament dimensions.

Table 3. Correlation between stress regulation, children’s SEN and temperament.

	Children without SEN	Children with language disorders	Children with self-regulatory difficulties	Children with severe disabilities
Negative Affectivity	Mean 4.27 Sd .48	Mean 4.42 Sd .49	Mean 4.16 Sd. .47	Mean 4.07 Sd .13
Effortful Control	Mean 5.09 Sd .69	Mean 5.04 Sd .42	Mean 5.32 Sd .42	Mean 5.22 Sd .45
Extraversion/Surgency	Mean 4.51 Sd .49	Mean 4.33 Sd .29	Mean 4.50 Sd .33	Mean 4.56 Sd .57

We found no significant correlations between the children’s stress regulation biomarkers, SEN (status groups) or temperament dimensions. We also found no correlations between stress regulation and background information.

Discussion

This study revealed no significant differences between the stress activation of the children with SEN and that of those without SEN in the integrated ECSE groups. We also found no significant temperamental differences. Interestingly, these findings contradict those of previous studies and the hypotheses of the present study.

Early toxic stress is not only a concern from the perspective of the individual: it affects society as a whole. The effects of early toxic stress are realised throughout adulthood and the costs are high (Franke 2014, 390–402). Therefore, understanding stress and how to support children’s stress regulation is crucial for well-being. The present study deepened the understanding of children’s stress activation in an integrated ECSE environment.

Children’s outcomes, including stress resilience, are known to relate strongly to family SES (Williams Shanks and Robinson 2013, 154–170; Evans and Kim 2013, 43–48). However, the present study did not find any connections between parents’ SES and children’s stress activation. This may be because the parents of the children who participated were relatively highly educated, which was also reflected in their income level. This study found no differences between stress activation on the basis of gender. Some previous studies have shown differences (Pérez-Edgar et al. 2008, 916–925; McEwen 2017, 2470547017692328), whereas others have found none (Gunnar and Vazquez 2015).

We were particularly interested in children who had self-regulation difficulties, because their behaviour is described as being restless and they have problems settling down when needed. This kind of behaviour indicates that they might have deviations in stress activation. However, according to our results, their biological stress activation was no higher than that in the other status groups. Our findings might thus indicate that ECSE environments are supportive for all children.

Our previous studies of the integrated ECSE groups involved in the current study revealed high general quality when measured using the Learning Environment Assessment (LEANS) (Strain and Joseph 2004, 39–50) and researchers’ observations and interviews (Syrjämäki et al. 2017, 377–390; Alijoki et al. 2013, 24–47). High quality was verified using assessments, activities and classroom arrangements that took into account the individual needs of children. The interaction between the children and ECSE teachers was empathetic, and the teachers were highly committed to their work. The reliability of the quality assessment was confirmed by remeasurement and inter-rater reliability (Hallgren 2012, 23–34). We can assume that in high quality environments, every child has the opportunity to be treated and respected in a unique way, regardless of temperament or any kind of SEN. Everybody has the right to be an equal member of the peer group.

These results raise the question as to why no differences were found between the status groups. The explanation might lie in the high quality of these groups, for example, the well-educated staff. High quality ECE environments improve children’s well-being, social and cognitive learning, and school readiness skills (Reunamo et al. 2012, 363–381; Peisner-Feinberg et al. 2001, 1534–1553; Bakken, Brown, and Downing 2017, 255–269). They can actually be seen as an intervention for children from less advantaged backgrounds (McCartney et al. 1985, 247–260). Earlier finding suggest that high quality has compensatory effects on externalising behaviour in particular (Hagekull and Bohlin 1995, 505–526). This could explain why the children with self-regulation difficulties had no divergent stress activation. Earlier findings (Alijoki et al. 2013, 24–47) from this same context indicated that ECSE teachers were committed to their work and that their interaction with the children functioned well. This might equalise children’s stress activation, regardless of temperament or SEN. However, more research is needed on integrated ECSE groups to confirm these reflections.

This study examined stress activation, which is only a small part of the stress system. However, the results lead to reflection on the zone of proximal development (ZPD) (Vygotsky 1978) through the lenses of stress activation. ZPD can be described as the closest, most immediate psychological development that includes diversity of cognitive, emotional and social processes. When in their ZPD, children function at the upper limits of their current capability. Encountering new learning demands is alarming and stress inducing (Sajaniemi et al. 2015). However, it is possible to keep going if sensitive scaffolding is available. In other words, children need co-regulation for maintaining stress levels at a positive and tolerable range. Without adequate scaffolding, stress might become toxic. We assume that functioning in the ZPD means simultaneously functioning on the borderline of positive/ tolerable stress. In the zone of positive/tolerable stress, a child is free to be active, curious and ready to assimilate emerging skills. When stressors became more demanding, the child is in the zone of tolerable stress, where they need support and co-regulation from adults to keep their balance to prevent them drifting into the zone of toxic stress. SEN or temperament had no effect on stress activation, which indicates that the children in these integrated ECSE groups could function optimally in the zone of positive/tolerable stress.

This study added some new information about the biological stress activation of children with SEN. It was not related to different behavioural characteristics of the children. The significance of this finding is that regardless of the different temperaments the pedagogy should be designed so that each child receives support for joint activities with others. In this way, optimal learning in the ZDP is possible.

Limitations and future directions

This study had some major limitations. First, due to limited resources, we only collected the saliva data on two consecutive days and took only two samples per day. Therefore, the deficiency of the early morning samples meant we were unable to explore the morning peak. In the future, with more resources, it would be interesting to also explore this.

It would also be interesting in the future to complement stress regulation research in ECSE with other psychophysiological measures. This would enable us to obtain more information on children’s stress regulation. In addition, it would be interesting to observe how co-regulation manifests in these ECSE groups using qualitative methods, such as video analysis.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by the Jenny and Antti Wihuri foundation [grant number 170155].