You live in a bubble if you think MIAA kids are not re-classing at the 8th grade level in order to improve their chances in the lacrosse. Crabs and FCA are full of holdbacks.
If we are talking 8th grade into HS, 90% of what you are calling holdback on those teams means prefirst, which is all but the curriculum for privates now. Some that didn't do prefirst eventually repeat in middle school, where most of their classmates already did in elementary. Private school kids on average a year older than public. The top teams are mostly private school kids, and it is not some underhanded plot, just is a product of the curriculum differences.
