There are lots of ways to say school is over for the day, the school is on break, or the term has ended:
The school day has ended. School has let out for the day. The final bell has rung.
Spring break has started. We've gone on break. We're on a break.
The semester is over. The school year is over. School's out.
There are also many ways to say school is beginning again after a break. One formal way to say it is "school is resuming." One informal way to say it is "school is starting back up."