So how old are you? We don't do grades here i'm afraid. I suppose you can tell if he likes you because he won't ask you out in front of his friends. If they aren't around hes got nothing to prove to them. It's also quite easy to tell when someone is genuine. You need to recognise the body language, be cautious if someone is touching their face a lot and avoiding eye contact. Also, someone who is truly interested in you will be friendly with you at school and not just spring the question on you. I think you need to trust your instinct on this one, it's usually pretty accurate. Good luck.