Abstract
This paper highlights several issues related to the concept of efficacy, particularly with respect to augmentative and alternative communication (AAC) outcomes for children and youths with severe disabilities. The author recounts examples of his past and present research interests, using these to operationalize constructs such as treatment efficiency and interaction effects. The pitfalls of naturalistic research are discussed, along with some specific protocols and considerations that may be helpful in appraising AAC outcomes without compromising validity.