If your school has a Smoothwall firewall, depending on its setup you may need to include a firewall rule to support video calls.

Within Smoothwall go to Network - Firewall - Firewall Rules. In Firewall Rules, number 2 is Allow Internal. Hover your mouse over that option and select Edit. Next to the Services option select Create and add details per below screenshot. Then select the newly created service from the list and select Add and then Save Changes.