One solution is to use a Wi-Fi repeater; this is another device which extends the Wi-Fi connection in your home. Connecting it to your router via a cable means you can bypass the negative effects of the load bearing wall, as pictured here:
Putting the Repeater between classrooms should give close to 100% signal to all the devices that were having issues previously.
This method doesn't require any changes to your Wi-Fi devices either. Apart from the initial setup of the repeater itself, if will extend your existing Wi-Fi network, using the same Wi-Fi network name (SSID) and password.