it's a letter written to people who you know. To write an informal letter, you write the topic of the letter and then you write the reasons for writing the letter, i.e, for this you write the reasons why your school is excelling in academic work.
This should be in the body of the letter.
After this you write the summary of the letter. By conclusion.
This are the right steps to take in order to write a good letter. The introduction, body and conclusion of the letter must be concise.
