Project Summary/Abstract The proposed 5-year study uses a causally interpretable research design to examine the effects of the Sit Together and Read (STAR) early-literacy intervention on the short- and long-term literacy skills of young children with developmental language disorder (DLD). It also examines the use of caregiver-directed behavior- change strategies as a means to support caregivers’ implementation of the intended treatment strength. STAR is a fully manualized intervention that significantly improves the early-literacy skills and longer-term reading outcomes of children at-risk for future reading difficulty. The proposed study is instrumental in assessing longitudinal impacts for children with DLD and identifying ways to enhance caregiver implementation of the key intervention ingredients. The study features four planned variations with each involving 80 caregiver-child dyads (total N = 320, 80 per condition). Two planned variations allow examination of the main effects of STAR for children with DLD, with 80 caregivers assigned to implement STAR for a 15-week period as compared to an untreated control. The outcomes of interest for these variations are children’s short-term print-knowledge development, literacy trajectories to two-years post-intervention, and reading-difficulty status. Two additional planned variations allow examination of effects of caregiver-directed behavior-change strategies (rewards and encouragement) on STAR implementation as compared to caregivers who do not receive any change strategies. The outcomes of interest for these variations are caregivers’ implementation of the intended treatment strength as well as mediated effects on children’s literacy outcomes. Child outcomes are based on direct assessments of literacy skills captured at six time-points, from study baseline to two-years’ post-intervention; assessors are blind to condition. Caregiver implementation is captured via logged sessions on a bespoke app as well as analyses of audiotaped sessions submitted via the app. Directional hypotheses are threefold. First, we hypothesize that children whose caregivers implement STAR will show significantly greater print-knowledge gains over the 15-week intervention period, and accelerated literacy trajectories through first grade. We speculate that STAR exposure will also significantly reduce the rate of reading difficulty among children. Second, we hypothesize that children whose caregiver implement STAR and receive one of two behavior-change strategies will show significantly greater intensity and dosage of implementation relative to those not receiving these strategies. Third, we hypothesize significantly greater print-knowledge gains and literacy trajectories for children of caregivers receiving behavior-change strategies, and that these effects are partially or fully mediated by intervention intensity and/or dose.