A single-case (B-C-B-C) experimental design was used to evaluate the effects of the Color Wheel classroom management system (CWS) on on-task (OT) behavior in an intact, general-education, 2nd-grade classroom during transitions. The CWS included three sets of rules, posted cues to indicate the rules students are expected to be following at that time, and transition procedures for altering activities and rules. Class-wide data analysis showed large, immediate, and sustained increases in OT behavior when the CWS was applied, with OT behavior returning to baseline levels when typical classroom management (TCM) procedures were reinstated. Each student's average phase data also showed increases in OT behavior when the CWS was applied and re-applied, and showed reductions when the CWS was withdrawn. Discussion focuses on evaluating the internal, external, and contextual validity of class-wide remediation and prevention procedures. (Contains 4 figures and 4 tables.)