I would say that it is a calendar year. If he is available during the summer, but the pack doesn't meet, he should still get credit.
So if he starts in May, it ends in May.
Venturing Crew Adviser, Assistant Scout Master, Renegade Merit Badge Counselor
Owl-2 WB 92-49
Foothills District Atlanta Area Council
I never teach my pupils. I only attempt to provide the conditions in which they can learn.--Albert Einstein