Why does OH!Raphael hate school so much?
A couple reasons.
One is that he didn’t really understand how things were taught, particularly when it came to “standardized” education. He's better at learning and paying attention when he can be more active or there's something to do or it's made fun in some sort of way. For example, when he listens to Donnie explain something (who usually does so in a more entertaining way) he understands a lot better. But because he was often told to sit still, or made to pay attention to what he considered a boring lecture, it was difficult for him to keep up.
Two is that because of reason #1, he was often labeled as a “problem student.” He had anger issues as well and would often get into fights, so this didn’t help with the label either. There were very few people willing to listen to or work with him on these issues, nor did he have any encouragement to learn, and so he views school as a failed system, largely because it failed him.
Despite this, Raph actually likes learning. And he’s rather observant and picks up on things that others don’t sometimes. He just needs to have an interest or motivation in something to pay attention to it (don’t challenge him when it comes to monster movie or action film trivia). But if something at all seems “school-ish” then his brain kind of shuts that down and he seeks out things more stimulating for him to put his energy towards.