It will work with whichever network it is connected to. If you are having problems you have an issue with the network.
Is the network at the locker a public network or at least a network for members or something, as such the administrator may have placed restrictions on use that stop the Apple TV from working properly.
It is because your locker room WiFi login requires a browser-based web login: i.e. you ARE selecting the correct network to join but you never see the log-in page to input the password because your locker room system throws up a browser page in order to actually type in the requisite password. Apple TV does not come with any browser software e.g. Safari, hence you never get to the log-in page; however, Apple TV will say that it is connected to the network when you investigate Settings (which technically you are), but then you actually need to log onto the network by supplying the password. No browser = no browser-based web login.