What many parents do not realize is that there is a hormone that gets released when we are ready to wake and get up to go to the bathroom at night. Some people have it right away and others take several years before it kicks in. Until then, it is extremely difficult for them to wake up and go to the bathroom and they will sleep through the potty signals their brain is giving. The drugs do not help this. They only work in certain situations and the side-effects and risks of the drugs out-weigh the benefits for a child your son's age.
He is old enough to change in the bathroom and take care of his pull ups without others noticing. Send him with a wetbag or gallon size zip lock so he can discretely pack up his used pull up and bring it home so their is no tell-tale sign in the bathroom for one of the other kids to discover.
For long-term, you cannot change the hormones, but you can change the sleep cycle. It requires commitment on your part, but you can get up each night and take him to the bathroom. Do this at the same time each night. If he is already wet, back up the time by 15 minutes until you hid his dry time. Do this every night and create a habit for him (it takes 21 days to form a habit). Once his body gets used to the cycle of getting up in the middle of the night, he will learn to get up and go to the bathroom on his own.
Another thing to do is talk to him about what happens when he pees at night. Is he dreaming about getting up and going to the bathroom? If so, have him look around the bathroom and make sure it's his bathroom before he goes. If the bathroom isn't his or he is in a strange place trying to go, he needs to tell himself he is dreaming and needs to wake up. This has helped many children who think they are doing good and going to the bathroom instead of wetting the bed, when in fact it's all a dream!