Lots of ways to disable USB ports in bios and at the operating system level, additionally have a proctor watching to be sure everyone is in a word processor. Heck, ewaste grade computers can run a basic word processor, fill all USB ports except the mouse and keyboard with epoxy. Mount the computer in such a way the rear ports are inaccessible without it being very obvious what someone is doing and fill just the front ports (if they exist) with epoxy. Lots of ways to go about it.