Personally, I think this is foremost an "HR" issue and secondly a technical one. I would probably take a step further than just banning the device. The core issue is the human, so I would be trying to address the human issue directly.
I don't know which country you are in - but in most jurisdictions it is an an offence to deliberately cause disruption to someone else in the public ISM bands (which is what WiFi uses).
You can check this for your country, and warn the student that they are committing an offence, and the school may lay charges against them. I'm guessing the school has a policy for students who break the law in the school grounds?
My personal guess is that @alemabrahao is right, and this is most likely to be a de-auth style attack. There is very little you can do technically about this.
About your only option is to enable 802.11w (management frame protection) - HOWEVER - many IoT style devices and low-end phones have broken 802.11w implementations - and will experience all kinds of issues. Computers generally do support 802.11w.
https://documentation.meraki.com/MR/Wi-Fi_Basics_and_Best_Practices/802.11w_Management_Frame_Protect...
