IMO students should be take the class that maximizes the probability of getting a c * the probability of engagement. Note that this isn't "at least a c" but a just a c. There should also be weekly surveys the directly question the students engagement. No matter how important the topic, if the student isn't engaged then they aren't learning it and are better served learning literally anything else. Even if that means not learning to read past a 1st grade level for 5 or 10 years. Transferring classes should become the norm, once you lose engagement it is too difficult to get it back (and if half the class leaves then that teacher now knows what NOT to do)