Jill Barshay, via a kind reader:

Tracking, the practice of putting a small group of higher achieving students into separate advanced or honors classes, isn’t popular with progressive educators. Previous research has pointed out that it exacerbates inequality in our schools because higher income and white or Asian kids are more likely to get tracked into the elite classrooms. Students who aren’t chosen can become demoralized, or the curriculum in the average class can get too watered down. Great teachers and extra resources get steered to these honors programs, leaving the kids who need the most help with less. Researchers have sometimes found that lower-achieving kids are worse off in schools that track.