Abstract
Background: Children with speech disorder are a heterogeneous group (e.g. in terms of severity, types of errors and underlying causal factors). Much research has ignored this heterogeneity, giving rise to contradictory intervention study findings. This situation provides clinical motivation to identify the deficits in the speech‐processing chain that underlie different subgroups of developmental speech disorder. Intervention targeting different deficits should result in a differential response to intervention across these subgroups.
Aims: To evaluate the effect of two different types of therapy on speech accuracy and consistency of word production of children with consistent and inconsistent speech disorder.
Methods & Procedures: Eighteen children (aged 4;08–6;05 years) with severe speech disorder participated in an intervention study comparing phonological contrast and core vocabulary therapy. All children received two 8‐week blocks of each intervention. Changes in consistency of production and accuracy (per cent consonants correct) were used to measure the effect of each intervention.
Outcomes & Results: All of the children increased their consonant accuracy during intervention. Core vocabulary therapy resulted in greater change in children with inconsistent speech disorder and phonological contrast therapy resulted in greater change in children with consistent speech disorder.
Conclusions: The results provide evidence that treatment targeting the speech‐processing deficit underlying a child's speech disorder will result in efficient system‐wide change. Differential response to intervention across subgroups provides evidence supporting theoretical perspectives regarding the nature of speech disorders: it reinforces the concept of different underlying deficits resulting in different types of speech disorder.