Navigate to the School Settings tab.
On this page, you will see a 'Behaviour' section of settings that you can change.
The first option 'Custom Behaviours' will allow you to enable/disable teachers from creating their own behaviours.
If you would like to enable teachers creating their own behaviours, simply choose 'Chosen by teachers' from the drop down menu.
If you would like to disable teachers from creating their own behaviours, simply choose 'Chosen by school admin' from the drop down menu.
Once you have changed this, you will see the option flash green. This is telling you that the option you have chosen has been saved.