The current project examined school readiness outcomes of children participating in a preschool professional development initiative, Winning Beginnings Learning Circles, which focused on school readiness and teacher professional development. Children were assessed on knowledge and understanding of school readiness concepts in the fall and spring of each school year, and outcomes were reported back to preschool staff to be incorporated into teaching strategies. Preschool teachers and administrators attended monthly professional development seminars that consisted of workshops in child development and social-emotional health, parent engagement, and use of data as evidence-based best practices. Preschool assessment data from the first 2 years of the project showed significant increases in average scores from pre- to post-assessment on school readiness, self/social awareness, and quantity subtests. Kindergarten assessment data indicated that children who remained in the project for at least one full year outperformed comparable peers and the average for the school district they attended as kindergartners. The results highlight the potential of professional development programs and the importance of teacher quality in promoting positive outcomes for preschool children. (author abstract)