Project Summary Developmental Language Disorder (DLD) is a disorder in language learning and use that affects 7% of the population. Grammatical difficulties are a hallmark characteristic of this disorder during childhood. Long-term academic and quality of life outcomes are poor. The development of broadly adoptable techniques to remediate comprehension and production of complex syntax prior to attainment of fluent reading would increase access to the academic curriculum earlier and improve long-term outcomes of individuals with DLD. It is unlikely that recast therapy, the current standard of care, is delivered effectively within the constraints of current service delivery approaches and reimbursement models. Thus, there is a need to either demonstrate that recasts are a superior intervention method worthy of the effort required for faithful implementation, or to identify and develop an alternative approach that is feasible for administration to children older than 3 who are not yet fluent readers. Illustrated syntax stories i.e., specially constructed stories loaded with the target grammatical form that can be read aloud by a caregiver, could be that more feasible approach. Literacy, while not universal, is more accessible than recast therapy to a broad range of adults and high rates of input can be rapidly and consistently provided. This approach has previously been shown to increase the production and comprehension of passives, reported speech, and conjoined clauses in typical preschoolers and school age children. Our own preliminary data suggests that illustrated syntax stories could also be effective for children with DLD. Here, we carry out a randomized controlled trial, enrolling 140 children with DLD between the ages of 4 and 7 who score below 40% correct on the use of passives and object relative clauses. Children receive one of four possible treatments (recasts at home, recasts in the lab, syntax stories at home, syntax stories in the lab) for one grammatical structure for 10 weeks and then outcomes are re-assessed for both the treated and untreated structures. Comparison of the two different treatment approaches in the lab under dose controlled conditions informs us as to the mechanism of action for language learning. Specifically in Aim 1, we contrast interactive, feedback-based learning (recast therapy) with concentrated systematic exposure (illustrated syntax stories). In Aim 2, we consider the influence of the delivery mechanism on the ultimate dose delivered when treatment is provided by caregivers. We ask whether there is sufficient difference between the two delivery methods in terms of the dose provided by caregivers such that it cascades down to affect child outcomes. Combining outcomes data with quantitative information about the degree of fidelity and adherence and qualitative information reasons for these behavior patterns (Aim 3) will provide critical information about the circumstances under which these treatments can be p...