Great Discussion here, and I am with PG and Coach May when they say that there is no 100% right answer for every Pitcher. Each guy is different.
That said, we have been taking our training and advice from Tom House and all the collaborative research of the NPA, AMSI, the Titleist Performance Institute, and now the RDRBI (USC). Coach House says that the research is supporting that the BEST answer is for Pitchers to shut down from Pitching for 4-6 weeks at a time, at least twice a year. This should be a time of Active Rest -- a time for training and conditioning, but not for throwing.
Every kid is different, but in our experience, the Active Rest periods definitely help. When my guy has had good Active Rest periods (at least 30 days) he has been at his best, and most consistnet.
My guy is a big, thick kid, who is not a "max effort" Pitcher. This year, he began throwing with HS training in Dec of last year, and played right through to the end of July. We planned for him to shut down from Aug 1 to Sept 15.
The big goal of the Fall was for him to get to Jupiter in October. In order to make that happen, he had to come back active in mid-August so he could compete for the team he ultimately went with (he was off for roughly 2-3 weeks). By the time he got to Jupiter, he was visibly tired. At best, he was about 70% of himself. Tired, but not hurting.
No complaints mind you. We knew what we were doing. We knew we risked him being a little worn down ... and he would not have missed the opportunity to compete in Jupiter for the world. This year, the goal was to get there. Next year, he will be sure to have his late summer rest period.
He shut down as soon a Jupiter ended, and will not start throwing again in earnest until the first of the year. No holiday camps this year, as he is a Junior, and we want to make sure he is rested before starting the Junior Campaign.
For what it's worth.