Disruptive behaviour in classrooms is a significant challenge for learning in schools and a risk factor for students’ academic achievement and a significant source of teachers’ work‐related stress. Earlier research shows that clear behavioural expectations, monitoring students’ adherence to them and behaviour‐specific praise are effective practices to reduce disruptive behaviour. Although behaviour problems are common in middle schools, most of the interventions have been developed and studied in elementary schools. This randomised study evaluated the effects of a class‐wide intervention on classroom behavioural climate and disruptive behaviour, on teacher‐experienced stress and on the time needed for behaviour management in middle school. The classes were selected for intervention by their teachers on the basis of poor behavioural climate. The intervention was based on teachers’ cooperation; they collectively agreed on clear behavioural expectations, used positive feedback and, if needed, applied consequences in response to high rates of disruptive behaviour. The results indicated medium to large effects on classroom behavioural climate according to teachers’ evaluations, and somewhat more inconsistent effects on classroom behavioural climate according to student evaluations and in the time needed for behaviour management. The behavioural climate of the classes remained at a constant level during the follow‐up. The intervention was well accepted by teachers and students. The results suggest that an easily applicable intervention may produce significant improvements in classroom behavioural climate in middle schools.

Disruptive behaviours in classrooms pose a significant challenge for learning in schools and are, at the same time, a risk factor for students' academic achievement and a major source for work-related stress among teachers. Earlier research suggests that clarifying the classroom rules and behavioural expectations, monitoring students' adherence to them and using behaviour-specific praise are simple and effective practices to reduce disruptive behaviour. Most of the interventions have been developed for elementary schools, although behaviour problems tend to be more common in middle schools. This two-month pilot study using a prepost design evaluated the effects of a class-wide intervention on learning climate and disruptive behaviour (evaluated by students and teachers); on teacherexperienced stress; and on the time needed to maintain the positive learning climate in middle school. The classes were nominated for the intervention by their teachers on the basis of poor learning climates. The intervention was based on clear behavioural expectations for the students, positive behaviour support and, if needed, rapid actions in response to high rates of disruptive behaviour. The intervention was carried out by teachers, supported by monthly counselling meetings. The results indicated a large reduction in disruptive behaviour, in the time needed to maintain positive learning climate and in strain experienced by teachers while teaching the classes. The intervention was highly accepted by teachers, principals and (although to lesser degree) students. Although the lack of a control group in the design limits conclusions regarding the amount of change attributable to the intervention, the results suggest that an easily applicable and trainable intervention, which requires very little external support, may produce significant improvements in learning climates in middle schools.