Why can my pupils see other pupil trays?
This is due to the fact that the trays were created within Mini Mash itself.
When you create a tray using the add tray button within Mini Mash, this always generates a shared tray that is accessible by all pupils.
See How do I create shared trays that all pupils can see? for more information on how shared trays are created.
If you would like pupils to have private trays, similar to "My Work" folders in Purple Mash, you will need a Purple Mash subscription.
You can then generate these trays with the help of the steps in the guide How do I create a personal tray for each pupil?