This article examines the achievement effects of a prosocial classroom and instructional management program--Consistency Management & Cooperative Discipline (CMCD)--implemented at 14 elementary schools in a single geographic feeder pattern of a large, urban school district. State reading and mathematics achievement data were collected over 2 years for a stratified, random sample of 350 upper elementary students and their matched cohort. Using an archival post-hoc quasi-experimental design, test data were collected prior to start-up and upon program completion, enabling a continuous view of achievement from both groups. Students in CMCD schools outperformed control students. In mathematics, on average, CMCD students ranked at the 67th percentile, while control students ranked at the 50th percentile. In reading, on average, CMCD students ranked at the 64th percentile, while control students ranked at the 50th percentile. These findings are consistent with other studies of CMCD. As the classroom management program does not provide an academic curriculum, findings suggest that other alterable and additive educational variables that improve learning conditions should be examined further. (Contains 4 tables, 3 figures and 1 note.)