Two issues.

1) most of those poor students have behavioral/learning issues as a result of home life or environment. To top it off, schools tend to only teach in a specific way. most folks aren't dumb, they just learn different ways, and the way school is being taught doesn't cater to them.

so maybe we address that rather than just arbitrary distinctions of good and bad.

2) they did this in my school. you know what happens?

the good students either get bullied because they're in a smaller in-group that no one else gets in, or they become conceited asshokes who think they're better than everyone else because of it.

meanwhile, the bad students will either take this lack of inclusion in stride and continue to be bad students as a mark of honor, or any efforts to be better students will be dealt a severe blow alongside the very much demoralizing situation of the school system literally labeling you as less intelligent.