Anyway, this isn't the Economics forum. The point is, high school Social Studies routinely take the socialist (D) side of policy disputes without suggesting that the issue is controversial. The sociologist Daniel Reisman (The Lonely Crowd) argued (Commentary? I don't recall) that the pre-college curriculum not include Social Studies because, he suggested, many teachers would not resist the temptation to indoctrinate students.
I suggest the better option is some restricted definition of "school" that includes topics on which a large majority can agree (Math, basic language fluency, classical mechanics (i.e., 19th century physics), chemistry, vocational prep), and subsidize any school that provides at least that curriculum. Let parents append whatever (benign) additional curriculum they want.