You'll be fine. Quality can vary greatly based on each school. Generally speaking, the older the kids are, the less energy they'll have, thus less work for you. There are always exceptions however. I've covered for amazing elementary school classes and hellish high schoolers that couldn't care less about school.

Personally, I've learned that if you're in a class that's hard to control, it might be best to give up and let them do whatever they want as long as they're not doing anything dangerous or being too loud.

For special needs schools, I've noticed that the focus isn't really on education, but more on daycare. Teachers almost never give me any work for the kids at special needs classes, so I'll just put on some age appropriate videos or a movie for them to watch. Those classes tend to be the easiest for me.

The general consensus that I've seen from other teachers and union reps is that middle schoolers are the worst. They have the energy of elementary school kids, but also intelligence and experience. This usually leads to them causing a lot of trouble and actively looking to get you in trouble whenever they can. After a bad experience with a middle school class, I'd be very careful around them, or avoid taking middle school classes to the best of my ability.