I could be wrong, but isn't the person who diagnoses the one who reports to the health department? If you were the first one to assess and suspect then you would be the one to contact the health dept with a suspect case, and then the health dept would follow up with the parent/child and doctor for confirmed diagnosis. Right then and there I would be calling my supervisor and the administration of the building, with answers prepared.
Nurses don't diagnose. (Unless you are advanced practice)
However, back to protocol - I'm going to ask questions so that you can learn (and I'd have to look them up in my own setting if it happened, too, and make phone calls) what do you do when someone does test positive and has been exposing people in your school? How do you notify so that those who are not vaccinated for whatever reason can be monitored and excluded appropriately to keep the rest of the population safe. Always use everything as a positive learning experience, every day. Try not to panic and keep your head high. I wish you the best, my school friend.