How do I write a persuasive letter to my Headteacher?

I’m supposed to be writing a letter which will convince her to make me a senior prefect. (I really want to be one as I get to go to Alton Towersn next year!) ;p Here’s what I have so far. Please tell me if you have any ideas :)

I am writing to inform you that I would like to apply for the position of senior prefect. Offering me the opportunity to take such responcibility will help me gain the confidence that I need to confront others when dealing with a particular situation and will encourage me to improve imperfections as my attendence. I aspire to have a career that involves either musical or writing ability; this is vital if the skills to perform in front of other people and share ideas while discussing a topic are necessary. I understand that I am expected to set a good example to the younger students, and the polite attitude that I have towards people will help me achieve this. You can be sure that I can be relied on when a certain situation has to be controlled as I have the ability to see a situation from another person’s perspective, and avoid abusing the position to order others around without authority…

Please consider accepting me as a senior prefect…