Bump. As a high school math teacher, I've appreciated the relatively rational discussion, and would have put in my 2 cents earlier, but things are busy at this time of year
The idea behind the 'incomplete' grade is, as discussed, not without merit. It forces students to do the work before receiving credit. A major problem in implementing this, as is often the case with ideological solutions, is logistical.
For one, where do you draw the line on what constitutes non-sufficient evidence for credit? One assignment? One unit test? How will you get different teachers in the same school never mind the same system, to agree to a standard assessment plan? And, if you do not, you are leaving yourself wide open to grades being challenged by parents or students. We're not talking one test mark, we are talking withholding 5 credits which may prevent a student from graduating.
Moreover, when you withhold credit, how do you manage 'extending a course'? This may be possible in the lower grades where timelines are longer, but when you are in a semestered system, there are all sorts of complications. Second semester courses may require prerequisites, and a student being withheld credit will have to re-arrange their entire time table. Over the summer, teachers and students move on; how can you reasonably have a student come back and complete a course two months later?
At some point, the situation will come to a head. Either the student does the work by a practicality-imposed deadline, or he/she does not. The merit - and the failure - of the no-zero policy occurs here. Some students will, with their feet held over the fire, do the work. Others will still not. Can you then reasonably base their final mark only on work submitted? It would be blatantly unfair to other students, not to mention mathematically inaccurate, to state that this mark represents their understanding of the entire curriculum.
Thus, all avenues have been exhausted. The student does not pass the course. The end result is the same Ironically, Alberta Education demands a final mark. How do you calculate this mark? By entering 'reluctant zeroes'.
In essence, public education still works on the factory model. The end goal is to graduate as many students as possible, within a prescribed time period. For confirmation of this, look no further than the Alberta government's obsession with high school completion rates. Quality control is present (i.e. students must show understanding of a prescribed curriculum), and building individual relationships with students and parents is hugely important but in the end, we are still a system of mass education. A no zero policy is a good policy for 95% of your students, but as with any blanket policy, it will cause great difficulty with the remaining 5%.