write a letter to the principal of your school asking him/her to grant you leave for a family event
24 September 2013
Subject: Application for one day leave
This is to bring to your kind notice that I am ABC studying in class VI of your school.
I wanted to inform you that I will not be able to come to school on Friday 27th September 2013 because of an important family function wherein my presence cannot be avoided. I would be highly grateful to you if you'll grant me leave for one day. I assure you that I will definitely join back on the next working day.
Thanking you in anticipation.
VI - D