Hello Martijn and Yael,
I especially like the part where you mention: the best time to give feedbacks is during the learning experience (not when the work is finished and ready to be given a grade).
It reminds me when I was studying Math at school. I had the exact same feeling. I learned more during the after test correction because it targeted my own mistakes. But it was too late! I already had a bad grade lol.
Receiving correction during the learning phase is so much time saving and confidence builder.