Behaviour may not be an issue within your school, but that might not stop you from worrying about how the class will react when you are being observed.
Undoubtedly, all children will adapt their behaviour when another teacher is in the room.
This can result in a supremely well behaved class and nine times out of ten, it usually does. If you happen to experience the one time out of ten in which that is not the case, deal with the behaviour in the way that you normally would.
Stick to school’s behaviour policy. Don’t be afraid of stopping teaching to deal with a behaviour issue. As long as you remain calm and consistent, adverse behaviour shouldn’t be detrimental to the outcome of your observation.