Cross-posted from here.
Why does this happen?
It’s usually the result of a lack of learning in prerequisite courses – that is, students somehow being able to pass the prerequisite courses without demonstrating sufficient mastery of the material. The usual culprits are grade inflation and/or lowering of standards.
What should be the correct remedy?
The “correct” remedy is to hold the students accountable for learning the material in your course, including the prerequisite material that they are missing.
This requires the instructor to put forth a ton of effort supporting students through remedial assignments/assessments and help sessions while simultaneously “holding the line” in a hardcore way (i.e. you have to be a bit of a hard-ass). And of course it requires a ton of effort from students because they have to put in the extra work to pay off their “learning debt,” which is usually a rude awakening for them.
But what usually ends up happening instead is everyone turns a blind eye and pushes the problem further down the line: the instructor just gives the usual lectures/assignments, curves (or otherwise inflates) the grades, students go along with it, and the problem is left for their next instructor to deal with (or not deal with).