1234, West 67 Street,
Carlisle, MA 01741,
[Subject: Normally bold, summarizes the intention of the letter] -Optional-
Dear Austin Parker,,
I really must express my gratitude at the help you freely gave me in order to pass my Spanish class. I realize how busy you are and know that it took a lot of time to get me ready for the test. I know I was on the verge of failing the class and I could not get my head around the language at all. Your patience was much appreciated and it is through your help that I have managed to pass the class with one of the best marks.
You are the sort of family friend that anyone would be proud of.