Is your composer high schooler contemplating a summer program? Walden School in Dublin NH is still taking applications. Boston Conservatory has a shorter intensive that is also recommended.
It might be good to find a conservatory prep program, or as I wrote before, contact a school about private lessons.
The Juilliard extension program does include readings by Juilliard students, so that is a plus. The advanced composition class has this:
This course provides advanced composers the opportunity to work with multiple faculty members in the course of the year