When I worked at the college I did a lot of work on methods of learning and especially what constituted effective feedback from teachers. Again and again it was made clear that formative feedback - get the student to perform a task (be it an essay, a test or a practical task)/give detailed feedback on how it can be improved/student tries again/further feedback given - not only gets best results, but teaches the student how to best evaluate and develop their own practice, so they become efficient independent learners.

And yet, the number of teachers who actually do this is so small!