If one is coming on and you know you aren't going to be able to come down from it (prevent it), ask to use the restroom before it starts and go to the restroom to work on breathing exercises in private/where it is quiet. Best case scenario is that you could work it out with the school so that the teachers are aware you have panic attacks and you have a designated place to be excused to (counselor?) for your panic attacks. I have a lot of experience with this (I went through this) so PLEASE reach out if you need any help.

There are ways to stop a panic attack. Keep a bottle of water and some mint candies with you along with some sort of fidget device. Of course asking to be excused is always an option. If possible sit as close to the exit as possible.