Higher cost mostly because you need better teachers, and probably more of them (20+ kids per teacher makes it hard to give all of them what they need). Tracking

Higher cost mostly because you need better teachers, and probably more of them (20+ kids per teacher makes it hard to give all of them what they need). Tracking would help contain the costs because it's easier to teach 20 kids roughly on the same "level" in a topic than 20 kids some of whom are operating about three grade levels behind, and others three grade levels ahead.