You get a better ROI on the good students. They ended up with a better education at the end not being dragged down by apathetic/disruptive/clueless classmates w

You get a better ROI on the good students. They ended up with a better education at the end not being dragged down by apathetic/disruptive/clueless classmates while the less gifted students weren't made to speed through material beyond their level. Why don't you think it helped?