This summary describes the Head Start CARES research project, which evaluated three classroom-based approaches to enhancing children's social-emotional development: (1) The Incredible Years Teacher Training Program; (2) Preschool PATHS (Promoting Alternative Thinking Strategies); and (3) Tools of the Mind--Play. The three social-emotional approaches tested in Head Start CARES were called "enhancements" because they complemented and enriched classroom practices that already existed. The effects, or "impacts," of the enhancements were rigorously evaluated by randomly assigning approximately 100 Head Start centers to one of the three enhancements (the program group) or to a control group that continued with "business as usual." On average, coaches and trainers rated implementation across the year for each enhancement at or above a satisfactory threshold for quality implementation. Compared with the control classrooms, each enhancement also improved the specific teacher practice it was meant to affect: The Incredible Years improved teachers' classroom management; PATHS bolstered teachers' social-emotional instruction; and Tools of the Mind--Play increased the degree to which teachers structured peer interactions and play. Two of the three enhancements also showed consistent positive impacts on a range of children's social-emotional outcomes in preschool, although not always as predicted.