Since your son is relatively new to the process, and a sophomore, I would recommend trying a college program this summer. Coaching is an excellent and focused use of $$ when preparing for actual auditions, but you may want to try to decide if this “hook” has to do with actually studying various elements of theater - or being in shows. They are two very different things. I have known kids who have been in dozens of productions, got accepted to great college programs (b/c they are talented) and then leave b/c they didn’t understand that there was going to be actual classwork involved. This is especially true if his experience has been limited to school shows…in my experience they are not a really accurate reflection of the college (let alone professional) world of theater.
Here is a thread with info on a wide variety of summer programs
http://talk.collegeconfidential.com/musical-theater-major/122525-summer-program-big-list-data-info-keep-adding-p1.html