The present study examined the effects of tootling, a peer-mediated positive behavior intervention, on students' classwide disruptive and academically engaged behavior in three general education high school classrooms. A withdrawal design was used to assess the effects of the intervention. Students wrote tootles anonymously on paper slips and placed them into a marked container. A randomized independent group contingency was used to reward students. At the end of the class period, teachers randomly drew three of the submitted tootles and rewarded students about whom the tootles were written. Teachers also randomly drew the names of two students who submitted a tootle and rewarded them as well. All three classrooms displayed decreases in classwide disruptive behavior and increases in academically engaged behavior during intervention phases. Effect size calculations for both disruptive and academically engaged behavior indicated very large overall effects. The results of this study suggest that a modified tootling procedure utilizing a randomized independent group contingency can be an effective intervention for teachers to improve the classwide behavior of students in high school classrooms. Teachers found the intervention at least moderately socially valid and students rated it highly acceptable.