Here is a sample letter:
Dear [Teacher's Name],
I am writing to request a leave of absence for [number] days, starting from [start date] to [end date]. Due to [briefly mention the reason for leave, e.g., personal reasons, family emergency, illness, etc.], I will be unable to attend school during this period.
I apologize for any inconvenience this may cause and will make sure to catch up on any missed work as soon as possible. If there's any way I can make up for the missed classes or assignments, please let me know.
Thank you for your understanding and support.
Sincerely,
[Your Name]
Feel free to modify it according to your needs!