Of course they're not.

But splitting classes into easy and hard (and your school counselors, your family's finances and neighbourhood, your race, your sex, whether you're an immigrant and where from have a lot of influence on which one you're in) is very common. The boring easy classes and overly intense classes are both harmful in different ways. In "college prep" English we read Romeo and Julliet.... translated into modern English. Yes, that was as dull as it sounds. Classes moved slow and killed any potential interest in the subject.

EDIT: My understanding from kids I've tutored here is that before grade 9 classes aren't as split like they are in high school. I would guess kids who read more before high school are more likely to be part of the group in the higher level classes, and the workload is plenty to kill interest to read for fun