Yes, to do this please:
Log in and go to Play
Choose Multiplayer > Arena.
Select the Maths or Pastoral class (or choose "Whole School" if you wish to include students across different classes/years) you would like to spectate:
Click the 'spectate mode' button on the game you would like to spectate.
You're ready to go!
If you would like to play in the game and not spectate please click on the purple section of the bar, rather than the pink "Spectate Mode".