Disable wireless network card Mac OS X
You can move the IO80211Family.kext from /System/Library/Extensions. The Wi-Fi won't function without this file, so moving it will prevent the Wi-Fi from working. If you leave the file on an external drive, you won't be able to re-enable it without the file.

Alternatively, if you're able to disable the admin account, it's a bit easier. Go to System Preferences → Network → Wi-Fi → Advanced and require administrator authorisation to turn the Wi-Fi on.