Write the current date at the top of the letter. The student's name must also be listed prominently on the letter so the attendance office can easily distinguish who the letter is about.
Explain the reason for absence in the body of the letter. Also include the date of absence in the letter.
Sign the letter and include daytime contact information. Contact information is necessary in case the attendance office needs to verify the authenticity of the letter.
Deliver the letter to the school when dropping the student off on his next day of school. Hand delivering the letter will ensure that the school receives it in a timely fashion.