I never thought Deku is any giant of intelligence or smarts. He was a hero fan so he spent a lot of time studying them. He was weak, so he had to come up with strategies and occasionally think a bit, not just tank through fights and other activities. He's hard worker, so that certainly helps with studying, provided he spends time on it and not only on muscle and endurance training. Still, he is a nerd of a kind, so stereotypically he should be quite good at academics. I dislike nerd type characters who aren't.
I'd assume Bakugo and Todoroki (not to mention that Momo princess living in a mansion) might even have private tutors.
Mineta... Some intelligent people are total creeps, so why not. And it's not like Mineta would have friends to hang out with or anything. Since he's probably simply spending most of his free time home watching porn, he might as well study occasionally.