Ask the school's IT dept if their router has been WIFI-configured to fully connect to only certain machine identification codes, aka MICs. MICs are unique ids for each and every computer that the computer broadcasts to routers. Routers can also be WIFI secured without even having to use a password by simply setting it to only fully communicate with specific computers. If IT is using this type of WIFI security, ask them to check the MIC on your machine is the same as the MIC on their router. It's entirely possible that their router electronically burped and forgot your computer's MIC or the wrong MIC was entered into their router, especially if they've recently changed or serviced their router or its settings.

Jack E/NJ