Another part of the explanation, I suspect, is that effective educational practice is effective regardless of group membership. (teachermagazine.com.au)
Individual risk factors, with the exception of shy / withdrawn behavior, were significantly different across trajectory group membership for boys and girls, as was low - income status for boys. (link.springer.com)
And there are other ways in which schools set expectations based on group membership. (teachermagazine.com.au)