I‘m not super versed in sociology of education but I was always under the impression that over assigning was a real problem in undergraduate and collage setting (even in high school to an extent I heard last).

My post-modern mind went straight to thinking this was the system working as desired. We over-assign to weed out students of from lower classes such that they are more stressed and less likely to graduate, therefor maintaining a status quo of higher classes being more educated and more deserving of the fruits of the labor of the less educated working classes.