It's true. San Diego Unified explains it succinctly here. Every time a student is absent, the district loses money. I guess that makes sense when you think about kids playing hooky (or does it?) or if districts were to keep kids on the rolls even when they move. But when kids are actually sick, which does tend to happen, the district also loses money.
So, we have to try to convince students to come to school even when they are sick. I think the official stance is to tell the parents that they should bring the kids to school and if the child still feels sick, come back and get them. There are some obvious problems with this theory - not the least of which is that all the other kids are then exposed to the germs. Also, I'm not sure the parents are thrilled about taking their sick child school and turning around to get them again.
The kids then come to school sick, because we tell them to. Then they get each other sick, and get us sick. But we still tell them to come to school sick, just perpetuating the cycle. Does this make any sense at all?
But we (and I use that word loosely; I for one, tell the kids to stay home when they're sick) still do it, because the school loses money when a child is out, even if they have a doctor's note. I wonder how many less of us would have the flu if students got to stay home when they were sick!
As I've already mentioned, educators seem to always feel guilty when we get sick and have to take a day off. But I don't think this is the way to deal with it.