Read Only Mode is a feature in which you do not have the control of the watch.
You cannot change or edit any setting in the read-only mode. However, you can easily check the location of the watch and see the notifications.
This setting is enabled during the school time in order to avoid any disturbance in the school for the child so that your child can concentrate on his studies. Also, some of the settings of the watch are changed during the school time. This is in order to provide more security by providing some notifications to school when your child is in trouble. This indeed helps to make the child more secure in school and outside of school.