S.E.
Put him on a timed schedule to go to the bathroom. Every 90 - 120 mins. You can work that out with the teacher. I am a teacher and would work that out with you. Give him a little watch to help him remember. You use one with an alarm, but that's very public, unless there was a vibrating alarm.
Get him on a pee schedule.
As for night, buy Pull-up, Underjams (expensive!), etc. I buy what is on sale and in the right size. Mine is 7 and nothing physically wrong. She drinks nothing all day long for some weird reason and then pounds liquid from 5:00-7:00. Nothing we can do. We send water, Gatorade, etc. She just "isn't thirsty." We tell her to drink even if not thirsty, but little goes in. We've started rewarding for drinking her water at lunch. If she drinks her water, I put in a sweet snack the next day. She's honest. Once she didn't have a water bottle and I asked about it. She said it spilled, so she threw it in recycling. I put in a tiny treat w/ a tag that said, "Honesty gets rewarded too."
Stephanie