Finally, our information on teaching practices, which is based on in-class time use reported by teachers, does not allow us to distinguish between different implementations of teaching practices. In other words, a certain teaching technique may be very effective if implemented in the optimal way. But the strength of our approach is that it examines which teaching style turns out to be effective, on average, for teachers in general. Optimal teaching methods that cannot be executed by teachers in general may do more harm than good.