Children are more likely to modify behavior when comments are directed at specific behavior, rather than general actions. When possible, the child should be talked to privately.
Children also respond better when a teacher's comments are descriptive rather than evaluative.
By describing their own reactions as opposed to the student's behavior, teachers are more likely to be seen as supportive rather than judgemental. Comments are most effective when timed close to the behavior. Children are unlikely to remember feedback that is given long after the action or assignment is completed.