To use classes in the Classroom app, you need:
The Classroom app installed on the teacher device. For more information, see Apps Purchased in Volume.
Teacher and student iPads on the same (Wi-Fi) network and able to connect to each other directly via Bluetooth
Note:
If a student device displays as offline, the device may be outside of Bluetooth range of the teacher device.
In addition to the requirements above, you must ensure that teacher and student devices meet the minimum device requirements for use with Apple's Classroom app. For more information about device requirements, see Classroom requirements for classes created with an MDM solution in Apple's Classroom User Guide.