Couple things I'd like to add-
1st, as far as the step back goes- my son experienced this last season. He'd been training his ass off over the winter and when the season started was pretty much in peak form ready to roll. When HS season kicked in neither the workouts nor the practices were as rigorous as what he'd had in the off-season and as a result near the end of the season his velo was down and his pitches were suffering. He went the entire first month of the season without giving up an earned run and only allowing 9 hits. He gave up 10 hits his last game of the season! He learned his lesson with about 2 weeks left in the season and started working extra on his own (weighted balls, long toss, etc) , so by summer ball he was getting himself ramped back up and had a great summer. This year he's determined to keep working like it's the off-season and avoid the in-season dropoff.
2nd, the coach for the school he has committed to has already sent an email asking for weekly HS updates. Clearly they're expecting him to play HS ball of for no other reason than to make sure the kid they've verbally committed to giving money to doesn't start to suck.
3rd, Our local paper has a great prep sports department, and it's pretty cool to see his name in the paper once a week or so. I'm not sure that actually helps with anything, but it can't hurt, and neither can ending up all-conference, all-area and hopefully all-state. Opportunities he can only get if he plays in HS.