I would suggest asking for a sample lesson from teachers in the departments that your son is looking into – they can be honest and say, yay or nay you should apply. They can also give insight as to what type of things to include in prescreens and auditions.
Also if your student’s teacher has connections to a program this can be a huge plus. My son’s teacher is in the program he is going to and was a big advocate of my son. He helped him with his prescreen and preparing for the audition.
Apply to a balance of audition programs and schools that have a good music department, but are non audition. The audition process can be exhausting!