Here is a simple recipe to make students fail: create assignments densely packed throughout the quarter, and where each assignment relies on the previous one completely, so that it requires prior completion of the previous assignments before it can be started.
Then, consider the case of a student who has a bit of trouble with the course and who can only manage to do 90% of the work assignment in a given week.
On the first week, he will turn in 90% of the work.
On the second week, he will first need to complete the remaining 10% of the first assignment (for no credit), so he will only be able to turn in 80% of the work.
On the third week, he will first need to complete the remaining 20% of the second assignment (for no credit), so he will only be able to turn in 70% of the work.
and so on until the 10th week, when he will first need to complete the remaining 90% of the previous assignment (for no credit) and will then have no time left to work on the 10th assignment.
On average, for a 10-week quarter, his grade will be 50%, or a bit less if end-of-quarter assignments are weighed more heavily; that, in spite of having done 90% of the work overall.
Note that giving the option of turning in assignments a couple of days late does not help. The student is doomed.
Now, consider a student who only just manages to do the entire assignment in the time allocated, and imagine that after three or four weeks, there is one week when he is sick, or tired, or something, and only does 50% of the work.
Then, from that point on, each week he'll spend half the time catching up on the previous assignment and half the time on the current assignment, so all of his grades will be 50% from then on, and at the end of the semester his average grade will be 60% or so.