The objective of this project is to examine outcomes of a treatment intervention designed to increase functional use of complex (multi-clausal) sentences in school-age students with primary language impairments that impact literacy and academic achievement. The treatment protocol includes: (1) three types of complex sentences (adverbial, relative, object complement), (2) encounters with complex sentences in real texts and across all modalities (speaking, listening, reading, writing, and (3) activities that engage metalinguistic understanding of complex sentences. Specific objectives are to (1) document treatment effect in terms of size and scope of impact in decontextualized as well as naturalistic language contexts, (2) document the effect of treatment intensity (dosage), (3) explore effects of sentence complexity subtype and treatment outcomes, and (4) explore relationships between treatment outcomes and participant variables (pre-treatment knowledge of complex sentences, verbal working memory, and non-verbal cognition).