This study reports finding from an ex post facto causal-comparison study utilizing data from a multifaceted program evaluation of a professional development approach to classroom management known as Development Designs 1 and Developmental Designs 2 (DD1 & D2). Data from this program evaluation indicate that teachers implement a number of classroom management strategies at higher levels after participating in sustained professional development for 2 or more years as provided by content experts, that is, facilitators and coaches whenever the school's leadership is perceived as supportive. In addition, levels and degrees of program implementation in middle grades schools were found to be associated with improved school climate and student outcomes, again, with school leadership being a covariate. Attendance, behavior, and academic achievement as measured by state assessments and other adequate yearly progress criteria among high poverty middle grades schools were found to be associated with levels of DD1 and DD2 implementation and supportive school leadership. The model used to support this finding is robust whenever 50% or more teachers in high poverty middle grades schools implement Developmental Designs for 2 or more years. (Contains 2 figures and 1 table.)