Best answer by Airgetlam
But you've indeed raised a complication, being in a school and using a wifi signal from a router that you don't have access to. It is possible that while they appear to be the same SSID, they could be two different frequencies, and the router isn't passing the data between the two. One of the things I did on my own router is setup the names so that they were distinct, so one is called "Net2" and the other is called "Net5" so I could tell the difference. But it would have been just as easy to call them both "Net" and not worry about it. It's only special applications like Sonos that care about the difference.
Since you're in a school environment, you may need to talk to the school's IT department on this issue. If it were up to me, what I'd be doing is setting up my own personal travel router that connects to the school's wifi network, and creates my own personal wifi network for me to connect my phone, my computer, and my Sonos to. That way, I'd have a little more security, and keep anyone else on that school wifi from playing anything they wanted on my Sonos.