The development of an in-service teacher training package is described which has the aim of training primary and middle school teachers to use behavioural methods of classroom management. It is shown how the package evolved from the programme of experimental behavioural research carried out by the authors in schools over the last ten years. Emphasis is placed on the on-going evaluations of successive versions of the package. The package was continually revised until it could meet the criterion of bringing about measurable changes in observed teacher behaviour and in the behaviour of primary and middle school classes. Experimental findings supporting its effectiveness are presented and discussed.