The grammatically correct sentence would be "he is a shitty student." This is slang as well as vulgar language; if you were speaking about a student as a teacher, or as a parent of a student, to say it formally, you would say "he is a bad student."

Hello, No, not really. I would need more information or context. Other options - He is a good for nothing student. As a student, he isn't good for shit. Good luck!