Research conducted by Henk van den Hurk shows that teachers’ knowledge of effective instructional behaviour is of limited influence on their actual performance in daily teaching. Observing teachers within their own educational practice and the subsequent feedback in teacher training college, however, has shown to be effective in improving teacher instructional practice. Van den Hurk studied the effects of the application of a cyclic model for data-feedback in initial teacher training as well as in a master course for teachers. In the applied model, teachers are observed with standardised observational instruments, while teaching their own classes. Back in teacher training college they are supported in formulating specific points of improvement for their own instructional behaviour. Subsequently, in their own classroom, the students practice the skills they further have to develop. After a short while another classroom observation is scheduled. The use of this model has proven to lead to a substantial improvement of teacher instructional behaviour. It is remarkable that advances in the quality of teacher instructional behaviour are reached in a limited time-span of only several weeks.