This is obviously a lot more utopian than practical, as it probably wouldn’t work, but if we have a few schools across different sectors, people should be able to go to whichever they’d like, as most schools are, believe it or not, self-selecting. Sure, some people who “aren’t as frum” might want to go to the “more frum” school because it’s “better” or something, but if they really think so, it means that they have a respect for the frumness of the school and want to be like that. A kid who wears jeans wouldn’t want to go to Bais Yaakov unless she was okay with changing herself to fit the Bais Yaakov, because there are other schools which wouldn’t care if she wore jeans. There must be a reason why she chose Bais Yaakov. It works the same way the other way around- if a “frummer” family wants to go to a “less frum” (by the way, I use quotes around subjective terms) school for another reason, such as academics or some specific thing the other school has that the Bais Yaakov doesn’t, then they can’t expect the student body to be any specific way to suit them because they chose the school. But in both cases, there’s no reason why they shouldn’t be accepted, as they both WANT to be there.
If this doesn’t make sense, it’s because I’ve right now got a 101 fever…