You can make WiFi unusable, however. Or you could alter the classroom so RF cannot enter through the walls or ceiling. And turn off the wireless AP in the room during exam time.

I suppose convincing the university to alter the classroom in this manner could be difficult, but they could also see the value in having some exam rooms that are essentially faraday cages

Ethernet using cat5 cabling was specifically designed such that the cheapest hubs would just be RJ45 jacks wired together passively. So one could make a "hub cable" in theory.

Interestingly another instructable linked to the one he showed, was about how to use 1 cat5 cable to every jack in the house to support both phone and Ethernet data.

This person was apparently unaware of the fact that a phone cords 6P4C or 6P2C cable will happily fit into the wider 8P jack. (That is to say that phone cable will plug into Ethernet jacks by design).

Further the Ethernet wiring standard deliberately has pins 3-6 (which correspond to pins 2-5 in a phone style jack, which are the 4 that are normally connected in a phone jack) connected identically to standard phone cord. Further Pins 4 and 5 are deliberately unused in 100Mbs Ethernet, which is the one pair necessary for a single phone line.

Thus if you have a house wired for Ethernet but not phone, adding support for phones to all the jacks is as simple as using Ethernet switches that connect pin 4 of all jacks together and pin 5 of all jacks together, and then plug a pone line into one of the jacks in the switch. (I would actually be surprised if there were not Ethernet switches specially designed for that).