You'll need to go through at least the first four or five of these search results until you find on you are interested in. Then read up on that philosopher until you are confident you know what his beliefs are, how he acted in the presence of his students, etc. And THEN you'll be ready to write such a letter.
Once you've written it, be sure to repost, and someone here will be happy to comment on your ideas.
eastren philosophy to a pupile