Letter of apology to the Principal of your school expressing your regret for misbehaviour.
To
The Principal,
Green Field Public School,
New Delhi.
Madam
I am really very sorry to have misbehaved with my Science teacher in the class. When she was teaching us an experiment, I kept myself, busy in drawing something. She caught me in the act and made me stand on the bench. Now I think I should not have behaved like this. I regret and promise to be a very nice student.
Yours obediently,
[Your Name]
[Your Class]
[Date]