Classroom students go offline

I tried classroom with three different configurations:

1) teacher ipad (pro OS X 10.0.2) student ipad (air2 OS X 10.1 beta) all work well.

2) teacher ipad (pro OS X 10.0.2) student ipad air (OS X 10.0.2) or ipad 3rd generation (OS X 9.3) in app classroom (teacher ipad) students go continuously offline for 10-15 seconds.

3) teacher ipad air (OS X 10.0.2) student ipad 3rd generation (OS X 9.3) work well.

how can I resolve the problem in the second configuration?

Thank you