What do you do if you wake up in the middle of the night and can't get back to sleep?

It can happen for lots of reasons, but here's what I told my daughters to do and it worked for them.
Pretend you're acting in a movie. This particular scene is of you sleeping quietly, and the camera is focusing on you. You have to be convincing, so try to look like you're asleep and breathe slowly like you're asleep...get comfortable and then don't move. Try to look exactly as if you're asleep.
Before long they'd always be back asleep

Suggestions for getting back to sleep after waking up in the middle of the night:

Get rid of bright lights or loud sounds.
Get out of bed and move.
Avoid staring at the clock.
Avoid checking your phone or other screens.
Meditate or try breathing exercises.
Relax your muscles.
Keep your lights off.
Focus on something boring.

Hopefully you did get back to sleep and have a great day at school.