This is a letter for the Past. which means, the leave has been taken, but leave letter was not given. So, it is a letter written by parents for their son to his Class Teacher, requesting the teacher accept his absence due to stomach pain. Please note that this leave letter for the leave taken yesterday.
F/o Student Name, Class VII,
The Class Teacher,
Since My son had severe stomach pain, he was not able to attend the classes yesterday(yesterday’s date) . Kindly excuse his absence and grant him permission to attend the classes from today onwards.