Respected Sir/ Madam,
Most humbly, my name is ____________ (name) and I am a teacher of ____________ (subject) working in your Institute/ College from the last ____________ (duration).
Through this email, I would like to bring to your kind attention that I have been preparing for ____________ (higher studies/ course name/ exam/other) in order to gain more knowledge regarding ____________ (technology/ subject). Therefore, I request you to sanction me study leave till date __/__/____ (date).
I have completed all the tasks assigned to me for the month of __________ (month). Please, understand my situation and grant me the approval for the same. I hope that you will approve my request for study leave.
Thank you for your time and consideration.
_________ (Contact details)