What should i do about these kids bullying me at school?

It will get better you will meet so many new people in middle school. You will love it, you have so much more freedom. Just ignore him and walk away and pretend he's not there. If you act like he doesn't bother you then he will leave you alone. Now about your grades, in elementary school I always did bad like D's and F's. But once I got into middle school my grades changed. I was getting A's and B's which I never thought would happen. You will do fine. Good Luck :)