The Per-Pupil Problem

I was listening to an interview on WDET (and I can't find it now) but I think it was with the superintendent of the Wayne-Westland schools. [I do really like the show Detroit Today on WDET, and there is quite a lot of school news on it.]

Before this interview, I had not really thought about this particular aspect of school funding.
In the olden days (that would be pre-proposal A), schools were primarily dependent on property taxes, and that was heavily influenced by how much a particular school district was willing to approve. So the difficult aspect of this is that some school districts were much less willing to tax themselves, and there was a large inequity between districts.
There was also a plus to the property tax scheme. If enrollment went up or down a little bit, it generally didn't affect the district all that much, because probably property tax collections didn't change very much. 
The current system has (somewhat) reduced the inequities between districts--at the very least, it has brought the floor--the least-funded districts--up a lot. Now, however, that funding is tied to the number of pupils, and small changes get magnified. This is especially true when the majority of school districts in the state are losing pupils. Yes, people are moving out of state.
You might be thinking that "it seems only fair" that you should get less money if you have fewer students, but here is the problem.
Take, for instance, a district with 5,000 students. In year 1, they have 5,000 students, but in year 2, they lose 100 students and they only have 4,900 students. They just lost between 5 and 10 students in each grade (it varied by grade), and that is not enough to cut a single individual class. They still have to offer advanced math in the high school, and three 4th grade classrooms.
In pre-Proposal A days, losing 100 students out of 5,000 would not have affected their bottom line very much, if at all. Now, losing 100 students means losing something like 3/4 of a million dollars--without the capacity to cut equivalently, because remember--not all of those kids were 4th graders, so they can't cut all 4th grade classrooms.
What does this mean? As we look at revamping funding options, let's look at options that don't make school districts overly reliant on per-pupil fluctuations. Of course the number of students in a district needs to be taken into account, but it shouldn't be the only thing taken into account.