cball,
I am sorry to hear of your son's injury, as I know too well how hard it is for them when this happens.
When my son was a few months shy of 12YO and just prior to a growth spurt, he fractured the growth plate and partially tore the MCL in his throwing elbow while pitching his first inning in an April scrimmage game.
He was first put in a removable cast by ortho for 3 weeks. She then said he could start light throwing at that point. My wife and I thought that was a bit aggressive, but we deferred to her expertise. Well, after missing the first 3 games, he came back for a game, but injured it again - on a swing, not a throw.
He was told to rest it for 3 more weeks, which we extended to 5. After that, he came back and finished the rest of the season, playoffs and All-Stars. Obviously, no pitching, and only at 2B the rest. By the time All-Stars ended, we were just playing catch in the yard and he said it still hurt. So he DH'ed only during Fall Ball and we found a new ortho.
He recommended that my son shut down completely from all throwing (incl. football, gym class, etc.) for 3 months - which he did (and he became pretty adept at throwing lefty in gym class
). Then he did some light physical therapy for 3 weeks and was sent home and told to continue the stretching, tubing and light dumbbells every day through the winter. He faithfully complied and maybe missed a day or 2 per week.
So I wholeheartedly agree w/ the advice to shut him down completely for some period of time, then do some physical therapy to learn the proper form to do the tubing stretches, then continue from there.
Good luck.