How to limit any devices to appear on any Bonjour/Airplay capable devices close by?
There are a number of ways to do this, depending on your network setup.

You could as @tron_jones suggested use isolated networks or VLANs. Another way would be to setup the router so that each class room is on a different subnet i.e. 

10.0.1.0/24 for class room 1
10.0.2.0/24 for class room 2
10.0.3.0/24 for class room 3

mDNS / Bonjour does not broadcast outside of the subnet by default.

Either of these options should work, but require a non-trivial amount of alteration to your LAN, essentially there is no solution within the product itself.