Background/Context: There has been a growing realization in American education that the traditional focus on academics, particularly mathematics and English language arts, is insufficient to guarantee success in the modern workforce and society (Griffin and Care, 2015). Educators, policymakers, and researchers have correspondingly broadened the definition of student success. One effort is to formally develop the social-emotional skills of children. In addition to building valuable skills in their own right, social emotional learning (SEL) efforts has been linked to measures of student success, including improved academic outcomes and fewer behavioral incidences in school as well as longer-term outcomes such as improved wages and decreases in criminal behavior (Osher and Berg, 2018; Schwartz et al., 2022). Prekindergarten may be an opportune time to institute formal SEL instruction as it is a time of development when children are building the foundational cognitive structures that will support social- and self-awareness. Yet, rigorous studies of formal SEL curriculum in prekindergarten are lacking. Also missing from the literature are evaluations of approaches that combine a formal SEL curriculum with the supports and structures that researchers hypothesize are needed for effective implementation. Purpose/Objective/Research Question: This study is a quasi-experimental and implementation evaluation of the Positive Emotional Development and Learning Skills (PEDALS) program. The study answers the following research questions: (1) Is the PEDALS program being implemented with fidelity? (2) What factors influence PEDALS implementation? (3) What is the effect of PEDALS on child social-emotional and executive functioning skills? and (4) How do the effects differ by child characteristics such as gender, race/ethnicity, and age? Setting: This study takes place in prekindergarten classrooms in southeast Michigan (Detroit), western New York (Buffalo), and central New York (Syracuse). Prekindergarten providers in New York are a mix of school-based programs and programs in community-based organizations. Providers in Michigan are exclusively Head Start. The setting is limited to classrooms that teach three and/or four-year-old children. Intervention/Program/Practice: PEDALS is a two-year program that aims to operationalize the practices that researchers hypothesize are needed for effective SEL program implementation. The PEDALS model consists of five main components: the Second Step Early Learning curriculum, coaching support, child screenings, data use for implementation improvement, and sustainability planning. An initial training in year 1 introduces teachers and site directors to Second Step and the PEDALS program. Coaches visit sites twice a month to provide classroom and site-level implementation supports. Year 2 includes a refresher training, and coaching occurs once a year. Year 2 emphasizes sustainability planning. Research Design: The implementation study involves two rounds of classroom observations, surveys of teachers, assistant teachers, and site directors, and focus groups/interviews of teachers, assistant teachers, site directors, and PEDALS coaches. The impact study utilizes a propensity score weighting analysis. Classrooms that serve demographically and geographically similar children, but do not use PEDALS, were recruited as comparisons. Propensity score models will include baseline assessments, child demographics, and site neighborhood demographics from the ACS. PEDALS classrooms in the study were in their second year of the two-year program during the study. Population/Participants/Subjects: The implementation study includes 39 teachers, 27 assistant teachers, and 16 site directors. Teachers are majority female and white with about 12.5 years of early childhood experience (Table 1). The impact study sample is composed of 1,009 children in 77 classrooms, in 41 centers, across the two states. The sample comprise 531 PEDALS children and 478 comparison children. We do not yet have complete background data, but children are predominantly Black, White, and qualify for subsidies. Data Collection and Analysis: All data collection was completed during the 2023-2024 school year. For the implementation study, the study team trained local observers who rated Second Step lessons and teachers' use of strategies on a rubric (Table 2). The first round of observations occurred in October/November and the second round in January/February. Surveys were sent to all teachers, assistant teachers, and site directors in the sample in January (Table 3). Video interviews with site directors and teacher and coach focus groups were conducted with a semi-structured protocols during February/March. The implementation study analysis includes descriptive analyses of ratings from trained classroom observers and the surveys and will include qualitative analyses of the interviews and focus group data. The two outcomes of interests are SEL skills as measured by the Social Skills Improvement System-SEL (SSIS-SEL) and executive functioning skills measured by the Head Toes Knees Shoulders--Revised (HTKS-R). Teachers fielded baseline assessments in October/November and end-line assessments will be administered in April/May. Background administrative data is currently being collected and includes: gender, exact age, race/ethnicity, special education status, dual-language learner status, and tuition subsidy status. Findings/Results: The implementation study found that educators understood the PEDALS model, found it useful, expressed strong buy-in and self-efficacy in supporting children's SEL, and were satisfied with the training, resources, and coaching. Surveys and classroom observations found that most teachers used Second Step lesson components as expected, and lessons were of high quality (Figures 1-2 and Tables 4-5). Two areas of improvement include using strategies in interacting with a child experiencing a personal or interpersonal conflict (Table 6) and helping site directors more faithfully provide classroom supports and plan for sustainability (Figure 3). We cannot yet provide impact estimates. However, Table 7 shows that treatment and comparison students look similar on unweighted baseline skills. On the SSIS-SEL, comparison children averaged 83 and PEDALS children averaged 79 of 153 points. On the HTKS-R, comparison children averaged 45 and PEDALS children averaged 48 of 118 points. There is a substantial area of common support for the propensity score weighting. Conclusions: Implementation study findings suggest that PEDALS is largely implemented with fidelity. Many of the aspects of the program are being consistently implemented. Some of the more difficult aspects, however, such as helping children in moments of personal or interpersonal conflict and sustained administrative support are areas of improvement. Impact estimates will provide rigorous estimates of the effect of the program under conditions hypothesized as necessary for supporting young children's social-emotional development.