Dear Mr. Wang,
I'm very excited to write to express my thanks to you. When I think back the past, never could I forget your selfless guidance every day. You are the most respectable mentor of my life; however, I was the most troublesome student in the class. I was late for school, skipped classes, and even wanted to quit. So trouble making was I that people thought I was hopeless.
Nevertheless, it was not until you kept talking with and guiding me that did I realized I still could make a difference.
Now I'm admitted to Peking University. Without you, nothing of today would have happened.
Once again, I'd like to thank you and I wish you a happy life.