My school is a technical school that used to make ham radio communications (AM, I think). The thing is, we have a huge antenna that isn't being used. So, could we use it as a WiFi antenna?
Almost certainly not.
Every antenna has a range of frequencies it's designed to transmit and/or receive. A large antenna designed for amateur radio, like the one you're describing, would probably be tuned for frequencies in the kilohertz to low megahertz range. It would be completely ineffective for the 2.4 or 5.8 GHz signals used for WiFi.