D.B.
It's developmental. It has NOTHING to do with "training" -- feeling the urge when you're awake is totally different from when you're asleep. It's more common in boys.
My son was like yours - we decided he needed sleep more than he needed anything else. We didn't wake him up at 11 and 2 to go pee - it accomplished nothing except making everyone exhausted. We tried the alarm but all it did was wake him up after he was wet - so there was no point.
Our son had nocturnal enuresis until he was 11! Your son is 6 so he's totally normal. Put him in Good Nights or some other product, and let him sleep and grow up. Don't let him feel ashamed. A lot of kids have this - try to focus him on all the areas where his body HAS grown up. Every kid's body does different things in a different order.
If he gets to the point of not being able to go to sleepovers because of this, you can consult the pediatrician. We are not big on medication, but we did follow the suggestions of a pediatric urologist who told us there are kids who go through this through their teen years even. Our son used the medication (one pill at night) from 7-10, tried going off it, and the problem returned after about 1-2 months. So he went back on until he was around 11.5 or so, and went off again, with no problems.
We also put a waterproof pad on top of the sheet, and a 2nd sheet on top. (We used a leftover waterproof pad from his crib and put it in the "pee area" - worked fine.) Then if he was wet in the middle of the night, we could strip off the wet sheet and the pad, wipe him down with some wipes, throw on dry pajama bottoms, and lay him down on the second dry sheet - it saved a lot of bed-stripping in the middle of the night. This was over 10 years ago and they didn't have the Good Nights and extra pads then - now there are more products because this is so common.
The issue is shame and punishment. Don't go there, and don't let him do it to himself.