I am not a mechanic’s coach, but I’ve been around those that are, and have noticed a trend with these people.
First, these coaches are observers first. In that regard, they either notice something wrong - or - worth developing. When something just doesn’t sit right with them (coaches), they take the time to talk and rationalize. In fact, they rationalize a lot. Almost to the point of being a broken record. I’ve noticed a reasoning process with their charges that covers the why-n-what-for of now. They get to know the physical and mental aspects of their guys in a very personal way. I’ve seen these coaches spot an injury from the past that was being kept from them, and even a potential risk into the future. I have never seen the coaches that I dealt with simply take someone and say … " here, I’ll show you how to pitch…" Come to think of it, watching these men is like watching a mechanic talk to a customer with a car that has a certain problem. The mechanic will get in the car and driver it around the block, just to start the judgement process.
Second, regardless of what your son WAS doing prior to meeting this pitching coach, from the get go he should have had regular consoletations with you AND your son on what was going on and why. Evidently from you comments here, that’s not the case.
As a pitching coach (retiree) who managed more than anything, heck , if a guy tosses strikes for the majority of his tenure, I wouldn’t complain. In fact, if he holds his own, great! On the other hand, don’t forget that your son is only 12 and won’t be signing any MLB contracts new week, so I would suggest sitting down with this pitching coach and have a friendly conversation of where your son is, where he came from in the beginning, where he is now- ability wise, and what this coach thinks that your son so look forward to during his next session. I would also suggest that at the end of each session, a progress report be given to you so you and your son can hash out any questions or issues for the next meeting. ,