A.G.
IS there a physical reasonhe can't? Can he pedal a bike? If he can it most likely rules out a physical reason.. something to do with muscle developement.
Other than that
#1 throw out the pull ups.... (let him see youdo this)
#2 keep him in UNDERWEAR all day no more pull-ups
#3 Stay consistant
#4 don't make a fuss over accidents simply tell/help him cleanup into fresh clothes(stock up on laundry soap)
#5 after he falls asleep for the night IN UNDERWEAR pull the pullups oput of the trash and HIDE them... If he peees at night you can put one onhim inhis sleep...
#6STICKERS may lead to a bigger treat like a new toy buy one with him and tell him if you have no accidents for 1 week youget the prize &
#7 give him prize if he ar least improves to one or two accidents a day.. Hey this ain't the military and he is getting the point
#8 If you live in the country where he can pee on trees or in mud puddles that will help Or cheerios (any cereal that is O shaped will work)make great targets.
I hope this helps and keep us up dated :)