Make eye contact and offer him a little grin if you realize he is staring at you. If he returns your smile or maybe makes a goofy face, it could indicate that he is intrigued. You may even mouth something at him, such as "Stop it!" or "You're so odd," to see whether he laughs or attempts to respond. If he keeps coming back your gaze, let your body language show him that you like being around him. A little shoulder bump or head nod might be enough to get his attention. Then, look him in the eye and give him a quick smile. If he responds with one back, you've got a match made in middle school.