How To Write A Formal Apology Letter To A Teacher . Acknowledge what you did that was wrong, and why it was wrong. Apology for talking in class. How to Write an Apology Letter to Your School Teacher Sample Templates from www.sample-templatess123.com Apology for the bad behavior. Here are some simple steps you can follow to help you write an effective apology letter: Dear name of teacher, this letter is to formally apologize to you for my behavior in class on date.