Research supports small-group emergent literacy intervention to boost preschool children's early skills and provide a solid foundation for continued literacy learning. Although such interventions are increasingly available to preschool teachers, we have limited understanding as to how these are implemented under routine conditions in authentic classroom settings or of the factors that facilitate or hinder implementation. In this study, we examined implementation of one small-group emergent literacy intervention, the Nemours BrightStart! Program, as used in 36 preschool classrooms (25 schools/centers) whose lead or co-lead teachers voluntarily agreed to participate; all classrooms served children identified as being at risk for later literacy difficulties. Classrooms were randomly assigned to one of two implementation models, with either teachers or other adults ("community aides") providing the intervention to small groups of children identified as at risk for literacy difficulties. Research staff assessed implementation using a multi-dimensional framework, with data derived from videos of intervention lessons and lesson logs submitted by instructors and instructors' responses on an end-of-year questionnaire. Data were analyzed using quantitative and qualitative approaches. Overall, instructors implemented the intervention such that it was delivered with high quality, afforded participant responsiveness, and aligned with the intended lesson duration. Adherence (i.e., extent to which key lesson elements were present) and the number of lessons implemented were more variable, with teachers generally exhibiting better adherence but community aides providing more lessons. Factors reported as facilitating implementation pertained to aspects of the intervention itself, such as the structured multisensory lessons and their interactive nature, or the ability to prepare lessons ahead of time. Time, classroom, and behavior management were commonly reported as challenges. Findings have important implications for intervention development, use, and scalability. [This paper will be published in "Early Childhood Research Quarterly."]