While school is regarded as a time that a student must without a doubt attend all classes, there comes a time when he/she cannot help but skip either a class or an entire day or more. Since school-going students are young and cannot be expected to handle a letter about missing class, parents need to take responsibility instead.
Some students no doubt, forge their parents' signatures, often skipping class for reasons that aren't morally accepted or supported otherwise. In such cases, schools must make it a point to call the concerned parent/guardian of the student and verify the authenticity of the letter and signature. Older students can, of course, write these letters on their own, but getting a guardian or parent's signature is in most cases an absolute need.
Excuse letters are required when you need to explain the cause of a past or future absence from a university or school. On the other hand, for students who have not attained maturity or are minors, providing a written application (a format provided by the school) becomes necessary. Usually the excuse letter is prepared by either parent, or guardian but in the case of medical emergencies, medical certificates/notes will need to be produced.
Beginning: Begin by writing the date on the top right or left corner. A handwritten LOA note is always better for the chances of it being a forged one is lower. Eight times out of ten, a teacher with an experienced eye is in a position to differentiate between an authentic note sent by a guardian and a forged one on the basis of the handwriting. Of course, that doesn't always mean that it's foolproof.
Subject: In between the date and the salutation (Dear Madam/Sir,), write the subject line after a little space. In some cases, it is placed under the salutation and the body of the letter. It generally begins with "Re:" (meaning "In regards to") or just "Subject:".
Addressing: Depending on where you place your subject line, write the name of the person to whom the letter is being addressed after a line's gap. Such letters are generally addressed to the class teacher, principal, or professor.
Body: Here you have to put down the subject matter in detail. The who, when, and why type of questions need to be answered. The content should be to the point, crisp, clear, and must state the reason and duration of absence along with the concerned dates (whether past or future). What's more, any additional information like bringing to their notice assignments that the child has missed should be addressed.
Conclusion: Finish writing the letter with a 'Thank you', followed by an apt salutation like 'Yours sincerely' or 'Yours truly'. Be sure to sign the letter followed by your name written in block letters right after, since the letter will not hold any legitimacy if you don't provide the former. If the absence will be prolonged to some illness, it is advisable to attach a medical certificate as previously mentioned.
You can put your phone number on the letter as well, in case the teacher requires it for any question. This will rarely happen but will add assurance that your excuse is genuine. Whether your child has missed one class, a day, or more, you need to write an excuse letter that states the reason for the same.