You're right...most kids who have been playing for a few years at a competitive level will be playing with kids outside their school. But for kids new to the sport, especially the youngers ones, I do think it matters for some. How many? Maybe there's research on it. Anecdotally, a few classmates of my kids chose not to play soccer because they couldn't play with classmates. I also know kids who decided as a group to play a different sport just so they can play together. Exceptions? Maybe. But for a sport competing against basketball, baseball/softball, football, etc., for hearts and minds, I think it will help attract more kids at the early ages.