General language performance measures in spoken and written narrative and expository discourse of school-age children with language learning disabilities.

Language performance in naturalistic contexts can be characterized by general measures of productivity, fluency, lexical diversity, and grammatical complexity and accuracy. The use of such measures as indices of language impairment in older children is open to questions of method and interpretation. This study evaluated the extent to which 10 general language performance measures (GLPM) differentiated school-age children with language learning disabilities (LLD) from chronological-age (CA) and language-age (LA) peers. Children produced both spoken and written summaries of two educational videotapes that provided models of either narrative or expository (informational) discourse. Productivity measures, including total T-units, total words, and words per minute, were significantly lower for children with LLD than for CA children. Fluency (percent T-units with mazes) and lexical diversity (number of different words) measures were similar for all children. Grammatical complexity as measured by words per T-unit was significantly lower for LLD children. However, there was no difference among groups for clauses per T-unit. The only measure that distinguished children with LLD from both CA and LA peers was the extent of grammatical error. Effects of discourse genre and modality were consistent across groups. Compared to narratives, expository summaries were shorter, less fluent (spoken versions), more complex (words per T-unit), and more error prone. Written summaries were shorter and had more errors than spoken versions. For many LLD and LA children, expository writing was exceedingly difficult. Implications for accounts of language impairment in older children are discussed.