The much anticipated "classroom" experience with 7*7 video streams is coming in public preview soon. There might be a few things you need to train your users on:
- It is not turned on by default for meetings
- Users may turn it on/off at any time during a meeting
- It requires at least 10 active video streams to be available
The large gallery view will be available behind the three dots on the control bar (...) for the active meeting. This is all according to a message in the message center recently, and in the road-map ID 65333. According to the road-map, the release of the feature has been moved to August.