You can always subnet a network down.. so that is a /23 so logical break would be /24, since your at 10.2.5 the break to /24 would create 10.2.4.0/24 and 10.2.5.0/24
Here is the thing.. What exactly are you going to do to subnet it down.. They are not routing that traffic to a routers of yours are they? You are directly attached would be my assumption.. So unless you have some router in your classroom and they route that network to you via some other transit..
Then while sure its easy to subnet any network into smaller networks - your problem is more involved… And without more info its impossible to advice you what direction to go into.
But if all you want is an isolated wifi network you could control - this would be as simple as connecting your typical wifi router which would nat the wifi clients to whatever IP it gets from your 10.2.5/23 network when you plug its wan in.
Better would sure being this with pfsense box and some APs.. But any 20$ soho router you pick up at the computer store would be able to create an isolated wifi network on your current network.