This study examined the impact of the use of cooperative learning on classroom discipline in third-, fourth-, and fifth- grade classrooms. Data were collected by means of teacher and experimenter observations of student classroom behavior. Problem behaviors were classified into two categories that involved the students themselves: off-task and noncompliance, and two categories that involved other students: bothering others and aggression. For cooperative and noncooperative classrooms respectively, teacher observers counted 36 and 50 off-task behaviors, 5 and 1 noncompliant behaviors, 32 and 35 behaviors that involved bothering other students, and 8 and 3 aggressive behaviors. Also for cooperative and noncooperative classrooms respectively, experimenter observers counted 40 and 59 off-task behaviors, and 37 and 36 behaviors that involved bothering other students. No noncompliant or aggressive behaviors were observed by the experimenter. From these data, it is concluded that the use of cooperative learning reduces the number of self-related off-task problem behaviors in the classroom. A list of 14 references is provided. Appended materials include a description of the behavior problems counted in the observations, a questionnaire for teachers concerning problem behavior, and a series of graphs illustrating the data described in the text. (BC)