I echo many of the ideas suggested so far.
I'll also share some unusual advice given to me when I really struggled at the plate (happened way more than I care to admit). This came from a player a couple years ahead of me who had an illustrious MLB career.
His suggestion? Pretend you have a hit and run on and slash the ball the other way. His reasoning?
He said when you're pressing, you get anxious and tend to leap out after the ball. Thinking about taking it the other way, as if the coach gave you a hit and run and you want to hit behind the runner, makes you stay back, letting the ball travel. This approach also gives you a game plan instead of merely having the negative thought of "please let me make contact" running through your head.
Please keep in mind that this doesn't mean you have to swing at the pitch (as in a real hit and run)...you are looking for a good (outside optimally) fastball to aggressively slash the other way.
This isn't a universal fix, but it worked very well for me and many other teammates. Your son sounds very talented. I'm sure he'll struggle through and be an even better player on the other side of this.