I added tags to this post to increase visibility.
I personally use Webex to perform remote troubleshooting.
If your education establishment allows you to VPN into their network, then you can simply enable remote desktop, built in to windows, and connect that way. However, this locks the screen and essentially you take control of the PC and the student just sees the login screen.
Another option is install a VNC server, a small app that runs in the background, and then when connected via VPN connect to the PC via a VNC client. This way the student can see you controlling the mouse and where you click etc. so you can explain what you are doing and why you are clicking where you click.