I subbed all grade levels last school year and in my opinion, high school is the easiest and most challenging. They will try to push you to the edge, but you stand your ground. Be firm and respectful. Even if you look like a teenager dressed professionally, like me, you gently nudge them back. Don't tell them anything personal or reveal your age. That is one of the biggest absolutely do not do things I learned while getting certified for substitute teaching.

Here's one of the most important things I learned: stand by or near the door when you're subbing for high school kids. They'll try to skip, but it's easy to watch them and teach from the back to keep them safe and in class doing their work. Wear very comfortable shoes because you will be on your feet for 45-90 minutes per period.

Last important advice: greet each new batch of students outside the door. You'll watch them greet you, then you'll be able to figure out if they're the kid who will try to skip/push you off the cliff. Try to learn their names when they enter as well.

Btw, I'm sorry this is scattered. It's pretty late here and I'm out of it. Good luck!