Abstract Children increasingly confront complex sentences as they progress through the school years. Sentence structures including passives and relative clauses are specifically mentioned in school curricular standards, and children encounter these in the context of conversations, books, and movies. For the 7-13% of children with a Developmental Language Disorder, the challenge posed by complex sentence comprehension and use can contribute to poor academic achievement and negative social interactions. Yet the bulk of oral language treatment focuses on vocabulary growth and grammatical morpheme errors in the preschool years, with scant attention to later-developing language skills. This grant proposes to compare two entirely new treatments for complex syntax. Two randomized clinical trials will test the effects of philosophically contrastive treatment approaches that represent opposing points on an explicit-to-implicit continuum of language intervention. We hypothesize that treatment methods in which children are taught to explicitly apply syntactic rules will produce high in-treatment performance, but at the cost of the automatic, implicit knowledge required for rapid and unconscious application to untrained linguistic contexts. Conversely, treatment intended to facilitate implicit learning of syntactic forms will result in incremental in-treatment gains but will ultimately result in a more generative knowledge and use of complex syntactic forms. We seek to replicate findings by conducting separate clinical trials for the treatment of passive sentences and sentences with relative clauses. In addition to supplying clinicians with much needed information concerning treatment effectiveness, the data will provide an important theoretical test of causal components of our recently developed model of complex sentence comprehension and use in children with Developmental Language Disorder. Health relevance The grant proposes to test new treatments for complex sentence knowledge and use, for which there is little in the way of effective intervention. The grant will directly test the efficacy of two approaches to language treatment (explicit training of language rules vs. implicit learning of syntactic structures) and will assess different models of the causal relationships among cognitive factors and treatment outcomes.