Question

how to write a complaint to your principal

Answer 1

you can use the following format:

To ,
The Principal,

Name of the School,
Address of the School,

Date

Sub:

Respected Sir/Mam,

1st para (Problem , its causes )

2nd para (resolution you want )

Thanking You,

Yours faithfully,
Your name
Class and section
Roll number.

You can use following starting and ending lines:
starting-I beg to say that I am a student of class__ in your school.
ending-I hope that you will take some actions in this regard at the earliest.