For typically developing children, the process that allows them to master their first language and to acquire adult-like forms by the age of five is well documented through a large body of research (Brown, 1973; Clark, 2016; Miller & Chapman, 1981). However, for children with congenital severe motor and speech disorders (MSDs) who use Augmentative and Alternative Communication (AAC) instead of their natural speech to communicate, the situation is much different. The field of AAC is relatively young and very few empirical studies have been conducted on the grammatical development of such children (Binger & Light, 2008; Sutton, Soto, & Blockberger, 2002). The goal of this dissertation is to raise the question: to what extent does the grammatical development of these children differ from that of typically developing children? To answer this question the dissertation is presented in two distinct but related studies examining the developmental patterns of 1) the production of early verb categories and their inflection and 2) the emergence of clause constructions. These studies were conducted by analyzing a corpus of four children, aged 9 to 13 years, with severe motor and speech disorders (MSDs) who used speech generative devices (SGDs) as they interacted with a familiar adult over the period of nine months. This corpus was collected as part of a larger study exploring the effect of conversation-based intervention on the acquisition of vocabulary and grammatical markers by these children (Soto & Clarke, 2017). Implications of this research suggest that children with severe MSDs and no evidence of cognitive impairment develop mental representations similar to typically developing children. This predicts similarities in the emergence of verbal categories, verbal inflection, and complex clause structures. Discrepancies in development are explained in terms of the characteristics and constraints of aided communication.