PURPOSE: The primary purpose of this study was to investigate child impacts following implementation of a comprehensive language curriculum, the Language-Focused Curriculum (LFC; Bunce, 1995), within their preschool classrooms. As part of this larger purpose, this study identified child-level predictors of expressive language outcomes for children attending at-risk preschool programs as well as main effects for children's exposure to the language curriculum and its active ingredients-namely, teacher use of language stimulation techniques (LSTs; e.g., open questions, recasts, models). METHOD: Fourteen preschool teachers were randomly assigned to 2 conditions. Treatment teachers implemented the experimental curriculum for an academic year; a total of 100 children were enrolled in their classrooms. Comparison teachers maintained their prevailing curriculum; a total of 96 children were enrolled in these classrooms. Teachers' fidelity of implementation was monitored using structured observations conducted 3 times during the academic year. Children's growth in expressive language was assessed using measures derived from language samples in the fall and spring, specifically percent complex utterances, rate of noun use, number of different words, and upper bound index. RESULTS: Children's language skill in the fall, socioeconomic status (household income), and daily attendance served as significant, positive predictors of their language skill in the spring. The impact of the language curriculum and LST exposure was moderated by children's classroom attendance, in that the language curriculum accelerated language growth for children who attended preschool regularly; a similar effect was seen for LST exposure. CONCLUSIONS: Adoption of a comprehensive language curriculum may provide a value-added benefit only under highly specific circumstances. Findings suggest that at-risk children who receive relatively large doses of a curriculum (as measured in days of attendance during the academic year) that emphasizes quality language instruction may experience accelerated expressive language growth during pre-kindergarten.