{Date}
Dear {School Principal / Teacher},
I am writing to you to request a leave of absence from class from {start date} to {end date}. I would not ask this favor if the situation were not utterly dire, but unfortunately {describe the unfortunate event, i.e. illness, death in the family, or so forth – make sure the reason you give really is dire}. I really must take a few days off to deal with this, and am sure you can see why it is necessary.
Thank you for your understanding. Again I apologize, but this was unavoidable, and I really have no choice.
Sincerely,
{Letter writer}
