I'm also having this issue with a student.
Wifi and bluetooth are on. We also had the same wifi. I'm a former genius and the tech specialist for iOS at my school, and I still can't get this working. It's a weird bug I can't figure out.
I reset network settings - Failed
I reset settings - Failed
Hard reset - nope
Restart the device - nope
I had her forget the wifi and rejoin. Still greyed out.
It's weird that she can type the code in but can't go further. Seemed to me like a permissions issue. No parent controls were setup on this device and all other students were able to join.
I'm going to keep this post bookmarked incase I find the answer.
Where you able to find a resolve?
Thanks!