It could be stress, or it could be that your little guy is just REALLY tired. My son is in first grade as well, and I have noticed it wears him out by the end of the day. He only did half days in Kindergarten, so this is a huge change for him, especially since he now has homework too. He also wet the bed one night last week, but lucky for me, he woke up before it hit the sheets. You are doing the right thing by cutting his water out an hour before bed, but I wouldn't make a big deal about this with your son. You may want to invest in some "Good Nights." Lots of kids wet the bed when they are bigger, and those will cut down on your laundry. I have a girlfriend whose daughter is 11 and still has a wetting problem. I also remember a girl when I was about 11-12 who had that problem, but she just wore special night time panties, and we didn't think differently of her. If you really think there could be something medically wrong, take him in for a check. It can't hurt. Take care.