I Am Frustrated

I have helped my boyfriend through everything he's been through, but I can't help him when he doesn't tell me what he's struggling with. I'm REALLY good in school, and he's struggling with his biology class, but can't tell me what concepts he's not understanding. I just want to be able to help him. His self-esteem is so far gone that he has no faith in himself, and when I try to encourage him, he snaps... I know he's frustrated, but he needs to have faith again...