Student performance doesn't entirely depend on individual circumstances, it depends on the environment and the other students around them. The special ed studen

Student performance doesn't entirely depend on individual circumstances, it depends on the environment and the other students around them. The special ed students require more resources. E.g. they usually have more staff, sometimes 1:1 aides, dedicated rooms, special classes. Beyond the resources explicitly allocated for them, they also take up common resources. E.g. if they are mixed into a normal class, the teacher usually has to spend disproportionately more time on them, either 1:1 in the classroom or in prep for customized learning plans. Informally bad students are worse in some ways since they don't necessarily get additional resource allocation (like an ESL or special ed student would), but will distract the rest of the classroom. It would only make sense if they completely segregated those students, which (AFAIK) is very bad for those students.