Mammele:
You wrote: “According to whose minhagim should they teach alef-beis and kriah? Leave it to the parents to teach? Maybe pick the supposedly most mesora based Yemenite version, that’ll satisfy everyone – not…”
Schools teach according to the way they read. A different הברה does not make a different Yid. I never once winced when my Rosh Yeshiva spoke with a different הברה than I did, nor did he. Since when does this issue become priority, enough to block one from being a mechanech or talmid? Can you cite a precedent in Shas anywhere? Sorry, but that will not become a barrier for me. You need to find another example.