School does not have to interfere with birthday plans for you and your boyfriend. Use school as a way to surprise him as a lead-in to what the day has in store for him. Incorporate teachers and friends into your plans to completely surprise your boyfriend with gifts and treats.
Make a scavenger hunt throughout school for him to find his gift. Start with a note on his locker that leads to the second clue. Make a different clue nearby each one of his classes so he has time to look for the gift between classes. Ultimately you should be waiting at the final spot with his gift in hand. Choose a spot that is secretive or a special spot for both of you.
Leave a card with every one of your boyfriend's teachers on his birthday. Inside the envelope write something you love about him to show you care. Insert a small gift into the envelope as well such as a gift card or a mixed CD. He'll never expect you to leave a card or gift with every teacher. Be sure to ask that the teacher give him the gift when he arrives.
Decorate your boyfriend's locker early before he arrives or after he leaves school the day before. Use balloons and streamers to show it's his birthday. If you know his combination, open his locker and place a gift in a hidden spot and hint around that maybe there is more waiting for him inside the locker.
If you are close to one of your teachers, ask to borrow her classroom during lunch. Order pizza and invite your boyfriend's closest friends for a pizza party. Do not tell him about the party before; instead, tell him to meet you at your teacher's classroom and surprise him. Top the party off with cake and gifts from all of his friends.