If you like a guy at school but are not sure if he like you then you should try to talk with him and develop a friendship first. Let him know that you are interested in him. There are many subtle ways to do this. You do not KNOW if he likes you are not. After you have told him you like him then yes, give him some space and let him decide what he wants to do with the information you provided. If he is interested then he'll come around to you. If not, then it may be good for you to move on. There will always be another man in you life before you know it.
Don't tell him you like him. If he doesn't know you that well, telling him that you like him will most likely creep him out, but in the slight chance he could say he likes you. That's bad, however, because he likes you without knowing you, meaning he is not interested in you for who are, but for his own selfish reasons. Instead, develop a relationship in order to find out if you really do like him and believe that you will have a worthwhile relationship with him. Then, if you still like him, you can analyze the relationship you have with him and see if he's recently made efforts to increase the level of your friendship to something more. If you have a good relationship with him, then you will be able to see if he's made advances easier than if he's made an advance when you and him aren't close in some aspect.
Don't do anything to make him like you, that's dumb. Be yourself. If he haven't noticed you yet, then move on. Don't be someone your not just to be noticed. That's called being fake. Never be fake. It's better to have someone like you for you then someone your not.