A study to identify variables between more or less effective student teachers tested student gains in learning a psychomotor skill. The student teachers were observed as they trained students to perform the "handstand roll over" in physical education classes. Observation focused on content of instruction, skill attempt reactions, management of task engagement, affectivity, and monitoring. It was concluded that time on task reinforces motor learning and depends largely on the teacher's choice of activities. Teachers' interventions and a high rate of success raised the time on task. Teacher effectiveness in producing learning gains was dependent upon the ability to transform time allocated for practice into individual student activity. (JD)