Could also connect a bunch of locks and put all the keys on a key ring. Lots of pictures of latch, lock, etc ideas for montessori type preschool. This lock one could be made with 2 boards, some o-rings, and some locks from Dollar Store.
Behaviour management "Calm down" is a phrase that we all use, especially with kids when experiencing intense emotions. Here are some alternative phrases that just might yield better results, and an action plan to put them in place.