If the parental values set down at home, if any are at all, are done so properly it really isn't going to matter if they are "force fed" something different.
It does more than you realize sometimes. I saw what it did to my kids...it can take a long time and many heartbreaking mistakes for a kid to come back to what groundwork the parent lays during those years when the school peer group takes over and the school is drumming nonsense in their heads. Youngest son is just starting to realize what Mom and Dad said is for real....I am not sure if oldest son will ever snap out of his adolescence.