And yes, I have also heard that once a white girl dates a black guy, white boys don't want much to do with her.
I agree that there is much more social interaction in the middle schools, and in grade schools kids seem to interact without regard to skin color.
The separation becomes more pronounced as they get older.
As for the after-effects of interracial dating... I concede that the impacts may be different in different areas. I'm in a rural area of the American South.