he might want a chance to get your advice on a problem or he might like you. he may be using this time to get closer to you.
in some cases, the guys asks you to wait for him after school or at a specific location. the location makes it sound like he needs to talk for longer than just a few moments. think about the location and environment. if it will be just you and him, then he might have something important to say (like his feelings about you) away from anyone else. if there will be other people there, he might just want you to wait around for him 