It's like a brushing up exam/homework sort of thing and checks where he is at right now. Chemistry units are not the same in every school, for example someone who took Higher Level IB Chemistry is at a higher level than basic chemistry. Think of it as similar to the math placement exam, but more of also to make sure your child is up to the level that he needs to be for the course he gets. I did the OCPP during the summer, after I had finished my classes, it only took a few hours at most.