Research on social and emotional learning (SEL) has largely focused on classroom interventions and student-U� and classroomU�-level outcomes. Few studies have examined wholeU�-school and district-U�level SEL implementations, or how to ensure that SEL programs are implemented effectively and sustained over time. This study examines both process outcomes and program impact as Open Circle is rolled out across a large, urban district over a three-year period beginning in June 2012. The study investigates the following research questions: (1) What are the critical factors to successful implementation of a wholeU�-school, comprehensive SEL program as it is scaled up across one third of elementary schools serving grades KU�-5 in a large urban school district over a three-year period?; and (2) How will the implementation of the "Open Circle Curriculum" and corresponding professional development influence school climate, teacher practice, students' social and emotional skill development, and behavior? The sample in this study includes over 7,000 students, 400 classrooms, and 23 schools. Primary data from the first two years gathered through classroom observation and student surveys in grades 3 and 5, Open Circle fidelity checklists completed by coaches and observers, semiU�-annual online surveys completed by teachers, administrators and school support staff, focus group and individual interviews with staff, and training attendance and coaching logs provide data to measure program implementation, school climate, and social and emotional development at the student, classroom, school, and district levels. Preliminary results indicate that this whole-U�school SEL program is highly scalable, reaching over 7,000 students with training for nearly 800 staff members at 23 district schools in a twoU�-year period. Key success factors have been robust wholeU�-school professional development, high quality implementation, initial and ongoing principal and district administrator support, and teacher buy-in. Forthcoming data will enable further conclusions about outcomes and impact. Tables and figures are appended.