I first read Merchant as a sophomore in high school, too- as an independent study, though. I knew what a Jew was, though, and was fully prepared to confront the nastiness even then. I agree that it sounds like a mess to try to teach it to non-Jewish high school students without any contextualization.

I re-encountered it in a college class as well, which was also the first time I saw the Darko Tresnjak production with F. Murray Abraham as Shylock, which I later saw again and wrote about in this post, as well as the Michael Radford film with Al Pacino as Shylock (which I dislike, because rather than turn Shylock into the story's tragic hero, it makes him a tragic victim, and I've about had it with Jewish victimhood narratives).