So, I did another one an hour later or so. I liked it much better than the last one. With the book, a lot of the stuff in the scene makes way more sense.
A: The gaze directions seem to be a very important to the picture, I think. The heads on the left are in more or less correct positions, the dead body is ok. The man just above the body should be leaning more to the left. Same goes for the man at the top right. That guy also holds some kind of paper and compares it to the book. There are a couple of hands visible: the teachers, and or two of the pupils. I have no idea where they are.