I have never understood this rule when you don't have any work left to do. You're not hurting anyone, you're not bothering anyone, and what if the student is working on something for another class?
STUDENT: (DRAWING RANDOM THING)
TEACHER DYKNOWING: WHY ARE YOU DRAWING INSTEAD OF DOING SCHOOL WORK?
STUDENT: GOOD QUESTION BUT WHAT ARE YOU DOING SPYING ON ME?
TEACHER: