At the bottom of the Edit Classroom page there is a flag that you tick if need to cancel a session.  You can add a note for the reason for the cancellation.  This note is not visible to end users, only admin users viewing this page.


Please note that you will need to cancel any registered users and also email them that the session has been cancelled using the Ad Hoc email feature.


Before 


 

After


Alternatively, if preferred, you can make the session NOT live by removing the tick from the Live radio box.