Abstract.  This paper is a study of normal and impaired (SLI) linguistic development, especially in verbal morphology and syntax. The paper studies both linguistic development and how developmental phenomena provide evidence for adult linguistic theory. We use extensive developmental data to test models of normal and impaired development that have been applied to other languages—in particular, the Agr/Tense Omission Model (ATOM). We develop detailed models of Dutch morphology that—together with ATOM—predict that Dutch‐speaking children will produce more root infinitives than English‐speaking children. Furthermore, the model predicts particular errors of tense and agreement will occur in Dutch but not English‐speaking children. These predictions are confirmed. We also investigate how developmental data can help us to solve a problem concerning the interpretation of features in adult morphology.

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Failure to meet language milestones from the age of 24 months was predictive of SLI, but the use of separate milestones had limited value due to low sensitivity.

Communication development from an intersubjective perspective: Exploring the use of a layered communication model to describe communication development in students with congenital deafblindness.

This study investigates the use of subject-verb agreement and verb argument structure in the spoken Dutch of monolingual Dutch children with specific language impairment (SLI) and bilingual Frisian-Dutch children with SLI. Both SLI groups appeared to be less efficient in their use of subject-verb agreement and verb argument structure than the control group (consisting of monolingual typically developing Dutch children matched on mean length of utterance in morphemes) in that they showed significantly more agreement errors as well as a relation between verb agreement structure complexity and omission, a relation that the typically developing children failed to show. Furthermore, no significant differences were found between the monolingual and the bilingual SLI group. These findings indicate that subject-verb agreement and verb argument structure are both affected in SLI, but not more severely in bilinguals than in monolinguals.