Dear Mr. President,
My name is (first name). I am a student at (name of school), and I am writing you today to share my thoughts about (issue).
(Paragraph describing how I became interested in the issue)
(Paragraph describing the issue and why it's important)
(Paragraph requesting a specific response or action from the president)
(Closing paragraph thanking the president for his work and his time)
Sincerely,
(First name)
(Name of School)
(City, State)