Had this happen with my son it ended up ruining his confidence and destroyed his development. Took his effectiveness away as a control pitcher with great "stuff" as they tried to turn him into a power pitcher. He went from great command and control to a two pitch very hittable shell "no-wonder, no mystery, next pitch fastball down the middle, eeekism".
Started with going from Hi-Low pitching strategies which most coaches don't even know what that means, to just rock and fire, goon-ism.
After spending countless hours and dollars having your kid trained you will find it all goes out the window with a coach that calls all the pitch locations and type of pitch. Pitchers are not allowed to use their own knowledge, brains and intuitive senses to get batters out. Pitchers have been reduced to 90+ mph pitching machines. Don't think, don't figure anything out for yourself just rock and fire. And you wonder why pitching is no longer like those we use to watch like Sandy and Drysdale. Coaches have killed the art of pitching.
If I were you I would take your son away from this goon and stay with the pro who has taught your son proper mechanics. As your son gets bigger and stronger the mechanics will serve him well as he gets into hitting with the wooden bats.
More great kids are ruined at the high school level then anywhere else in baseball development.
JMO