There are not enough subs to go around. How do I know this? Frequently I am called upon to go to another classroom on my prep period to cover for another teacher. This other teacher may also be out for the day, but the district was unable to get a sub to cover for that teacher. There can be two or three (or more) classes in this predicament. The more teachers out on a specific day, the greater the chance that I will get an "extra" period.
Today I was at the continuation high school. I figured I was safe.
I never (okay, there was that once) have covered an extra period at the continuation high school. All the teachers get covered. But not today.
So, I wondered about my luck. Friday I got an extra period, and there were not all that many teachers out (the teacher had to leave school early, hence needing coverage). And I kind of had that kind of week. The pay period was 9 days old (as of Friday), and I had worked enough to be paid for 10 days.
On the one hand, it's a good thing. I do get paid for that extra hour. But on the other, I kind of like having that period break. Especially when I'm fighting off a cold like today.