So for Freshmen and Sophomores at my school you can take CP (Easiest), CCP (Medium), and Honors (Hardest).
Basically CP are for the bottom of the barrel kids who are just about total burnouts headed towards community college.
CCP is a little bit harder and hosts the normal kids who aren't retarded, but also not geniuses.
Honors is the top of the line and has been bumped up a level this year to be somewhat more thought provoking, as opposed to the lower level classes where you simply learn the information and move on.
Once you're a Junior or Senior, Honors gets thrown out and changes to AP. Basically the same layout, but obviously AP will be more difficult than Honors was.
Unfortunately this system was basically just implemented because our student:teacher ratio was thrown off due to budget cuts. The higher level classes got harder and the lower levels got easier. We used to use a L1, L2, L3, and L4 system, but they switched it up and fucked over the students.