I have student similar to this. Find out if the behavior is occurring around the same time or not. If it is happening around the same time, it may be beneficial for them to take a brain break and take a walk to avoid frustration and hiding under the desk. If the problem continues, reach out to parents about concerns.

I think that paying close attention to what is happening around the student when they are hiding under their desk is beneficial. Identifying if there are any factors around them that may lead to feelings of fear, angst or becoming overwhelmed would be beneficial to avoiding this issue. If the problem continues, or you are not able to reach a conclusion by observing, reach out to the school counselor and have them meet with the student. You can also contact the parents and find out if this is something he does at home.

Giving the student tasks to help around the classroom can be a good incentive to help avoid the hiding under the desk. Tell him if he stays in his seat he can help pass out supplies. If he stays on task use whatever reward system you have in place for that class.

I think noticing signs as to when this occurs might help stop them in the act, if it is just for them to cause a disruption in the class. I think also if this is consistent behavior, the parents/ guardians should already know of the students misbehavior in class. I would maybe try to talk to them privately at a different time and ask why they do it, see if there is any accommodations or changes you can make of them to feel comfortable.

try talking to the student and seeing why they are doing this. Are they needing a brain break?

When behaviors like this are present, I think it is best to be direct immediately, so the student knows they aren't going unnoticed. A simple warning like, "John, that is unacceptable behavior, you will be walking 5 laps at recess if you do not return to your seat." If he doesn't respond after that, then I would continue through the lesson and conference with the student to explain what they did, why it's unacceptable school behavior, and what their consequence is.

I would definitely bring this up to the child's parents! This way, if the child does not fear you, they can still fear what you say!

Break cards could be helpful. Maybe having a designated safe space for him to sit at. You should focus on collecting more data on the behavior.

I would have a parent teacher conference if you have addressed the issue with the student and they do not respond to redirection. Working with the parents could give you the support you need to correct the issue with the student, or get to the root of why the student is misbehaving (attention, bored, anxious, etc..).

I would pull the student aside during downtime to ask why they choose to act that way. Some students will tell you what is going on. I would also check the students surroundings as well and around what time they begin to act out. I had a student act out at a certain time everyday and I found out it was because he was always anxious and needed to be on time for class or lunch. If we did not leave when he wanted to, he would begin to get anxious.

Maybe move the student to sitting closer to you or not at a desk in general. Find a solution rather than just saying stop. It can benefit the student too.

A possible solution is redirecting the student does not work, could be to move the student to the front of the room so he is in clear view of the teacher. This way he may feel like he can't get away with certain things if the teacher is watching him constantly.