What if instead of keeping children out of high school, it was a case of keeping kids out of school, period, for religious reasons? Let’s say you have a group of fundamentalist Muslims who believe, with the Taliban, that female children should not be educated.* They’re not running private schools or home schooling the girls in lieu of attending public school, they just plain aren’t educating them.
My gut feeling is that the courts would not consider keeping all females out of school a protected religious practice. Where religiously-neutral government regulation meets contrary religious practice, the rule is a balancing test instead of a bright line. The High Court’s opinion in Yoder was a complex and divided one, and THAT was with the court able to avoid the touchy issue of uneducated children because the Amish were sending their kids to grade school. The balance that favored the parents (or the religion, if you see it that way) when the issue was 4 more years of school would IMHO come out differently when the issue is no school or formal education at all.
To take my lawyer hat off and speak strictly as a citizen, the Yoder decision feels to me like a potentially dangerous decision to support group-based policy. What I mean by that is government dealing with minorities (religious and ethnic, not just racial) and groups as a single whole rather than as individual citizens and families. It seems to protect the Amish’s right to keep its members Amish over the right of the individual child to have an education that may allow them to leave the Amish. Generally speaking, I’m more than a bit wary when people talk about kids in an insular racial, ethnic, or religious group becoming educated and/or exposed to the modern world or general society and choosing to leave that group an as the “dissolution” or “dooming” or “extinction” of the group, with the kid (actually, typically either an adult or near-adult) having been “corrupted” or “seduced” by the modern or outside world. I don’t think we’re engaging in a lot of group-based policy in this country at the level of policy that actually gets adopted and/or implemented, but there seem to be extremists at both the far left and far right of the spectrum that treat certain groups as being entities to deal with (or, more scarily, TO) as a unified whole and not individuals, and push by various methods for policies on that pattern.
Group-based policy seems to create division and strife even where it’s designed to reduce it. Stuff like Lebanon, where the president always had to be of one specific religion, the prime minister of another, and (IIRC) the speaker of the parliament of another. It encourages people to think of others as Muslim, or Druze, or whatever instead of as individuals. Or Rwanda, where IIRC one tribe/ethnic group dominated the army while the other held positions of importance in business – an especially bad combination when “the ones with the guns” see “the ones with the money” as a group (responsible for the actions of the group) and not as individuals.
*I know that’s not generally considered “proper” or “orthodox” Islamic doctrine, but the Taliban think it is. IIRC my ConLaw class in law school, the gov’t can question (where relevant) whether a professed religious belief is really held by the individual in question, but to judge whether an honestly-held religious belief was “real” Islam, or Christianity, or whatever, would violate 1st Amendment-protected freedom of religion.