In the spring he can take MYHA skill clinics.
Marianne Watkins does 3 day clinics in Rockville (usually, Xmas, Memorial Day, Labor Day).
Nothing But Net runs a holiday clinic and a spring clinic in Rockville.
I can also recommend EHS Reston skill clinic (they have a holiday, spring break, and spring clinics). EHS is the best in the are (in my opinion), but, you may not want to drive out to Reston.