Please correct the sentences

Hi eteachers,

I wonder if the following sentences are correct. Please tell me the proper expression.
1. The recess bell has rung, all students proceed to your classrom for rest time.
2. Grade seven please assemble in the hallway to go to the assembly ground for the hoisting of the flag.
3.Excercise safty on the way home after school.
Thanks a lot.

Ernie