@prepschool2021, I understand what you are trying to convey. I also agree that your description is offensive.
The term you may be looking for is “dominant culture”. There are communities (and schools) in which the dominant culture is affluent, white, hetero, and sport-centric. It doesn’t mean everyone is this, but it does suggest that this group determines the norms and values. (The description above, btw, was from a study a college had done on itself as part of its work on diversity and inclusion.)
Operating outside of or in opposition to the dominant culture can be challenging. So in the example above, there might be an assumption that everyone could go home at breaks, afford to eat out in town, pay to store belongings over the summer, pay sorority dues, buy clothes for special events, or afford an unpaid internship.
Hard if you don’t have money! So it’s not a stereotype. Does that make sense?