First off I'd say take him to the barber shop and get him fresh (or just finish the cut urself) and let him know u only had his best interest in mind. Communication is key, whether u think he's cool with it and understands it or not, it's better to know for sure than to assume. Then I'd talk to him and try to find out what interests him and help him pursue that more. If he finds something positive that he can channel his energy into it could have positive effects on every aspect of his life including his grades. Maybe u've done this already, if so I give u props and I'd say just keep at it, but embarassing him in front of his friends that he's already trying to impress and fit in with isn't gona have many, if any, long term positive effects. Most likely it will just lead to him trying even harder to impress them, leading to worse performance in school and some dumb shyt outside of school.