This question already has an answer here:
I wonder if there is any way, how to turn off / disable the wireless network interface or driver, so I cannot connect to WiFi from running OS. I have MacBook Pro with OS X Mavericks.
The reason for this is I have some exams at the University and if I want to use my own notebook, I have to turn off the WiFi in some more permanent way (for example from BIOS, if I had PC).
I have installed rEFIt so I can enter to some kind of EFI Shell, but I honestly don't know, what I can do here to not destroy my computer.