My friends and I were in chorus and the teacher sent us to an earlier lunch and when we came back he was gone so we did this.

After we finished we wrote 'do not erase' and wandered the school before spending the last 10 minutes of class in my German teacher's room with his junior class.

In short, best day ever.

The juniors did this.

The teacher only let us in because he "already lost control of these ones" (direct quote from him).