This discussion of language assessment is based on the findings from a current program of research carried out in my lab in collaboration with Ken Wexler of the Massachusetts Institute of Technology and a group of talented student research assistants and staff personnel, supported by funding from the National Institute of Deafness and Communicative Disorders. In this area of investigation, we are exploring the grammatical abilities of young children with Specific Language Impairment (SLI) and the ways in which certain grammatical competencies differentiate youngsters with SLI from unaffected age peers and younger control children. One outcome of this line of investigation is the identification of a possible clinical marker for young children with language impairment.