1- Try to go back to the time when you had these struggles in school, and try to think what would have been the best advice someone could give you at the time? What approach would have been effective with you?
2- Then use that approach with your brother. Even if it’s awkward, you have to help him. Tell he will come across such challenges, but that you will help him find the strength to deal with it all. If you cannot directly talk to him about this, talk to one of his close friends and have that friend address it with him. Just make him aware of the dangers of those paths as best as you can, and share with him effective strategies to fight them.