This study examines ways in which teachers who are more and less effective classroom managers prevent misbehavior and deal with misbehaviors they cannot prevent. Six middle-grade teachers in a suburban, midwestern school district were observed during spring, 1988. Information on misbehavior in teachers' rooms was coded according to four categories: activity type; form of misbehavior; teacher response to misbehavior; and student response to teacher's desists (a desist is defined as a specific teacher action directed at stopping a student misbehavior). Three classrooms were rated as effectively managed and three as ineffectively managed. Effective classroom managers were those who permitted the fewest misbehaviors and were most successful in stopping misbehavior once it occurred. Teachers who changed activitites in the class or varied the type of lesson from day to day were able to prevent more misbehavior than those who did not. The most effective desists used by teachers were nonverbal cues (low level desists) and rule reminders (high level desists). A general discussion of the classroom management research is presented, along with an examination of studies that deal with desist strategies of teachers. Implications for definition of a teacher's classroom management effectiveness are discussed. Thirty-nine references are cited, and the coding instrument is appended. (RH)