Saying “thank you” hasn’t gone out of style, according to Emily Post’s Etiquette Daily. When your teacher goes above and beyond what is required, you can show that you appreciate the extra effort by writing your teacher a thank you note. Expressing gratitude to your teacher has farther-reaching benefits than the initial acknowledgement of your appreciation, too. It can increase your alertness and determination, make you feel more positive and build connections between you and your teacher, according to Dr. Robert Emmons in "Express Gratitude" on the Gannett Health Services website.

Short and Sweet

The “thank you” note doesn’t have to be long or detailed, but it should be specific, describing why you are thankful. You might write, “You didn’t have to let me retake this test, but I appreciate your willingness to let me improve my standing in this class. I’m grateful for the way you support your students.” Close the note by signing your name so your teacher remembers who gave her the note if she doesn’t open it immediately. In this example, your teacher gets the message that you know the retake was a courtesy. Your affirmation of the way she cares for the students in her class encourages her to continue to go the extra mile.

Write It Out

Typed notes don't feel very personal, so take the time to neatly write the note by hand to show your respect and gratitude. Choose a nice card or some attractive stationery. That makes your note a lot more attractive than one written on a sheet of paper torn out of your composition book or one written on a sheet of lined paper. It doesn’t have to look like calligraphy, but your teacher should be able to read it without an interpreter.

Waiting Is Ok

If you didn’t bring the note when you came to class to retake the test, don’t despair. It’s OK to send the note after the fact. The important points are to show your appreciation in a timely manner and to do so with style. It might take you a bit to decide what to say and to write it neatly. You could mail it later or drop it by her campus mailbox. Alternatively, find an opportunity to hand it to your teacher and add verbal appreciation to your note.

A Few Don'ts

Don’t gush or go overboard with the note -- it probably won’t change your grade on the retake. Don’t make the note too formal, either. You can use contractions and idioms when writing the note to make it more personal, but avoid making it sound like a tweet or text with improper spelling, advises the "Washington Post" article, "Are Writing Skills Necessary Anymore." Improper grammar, spelling and punctuation can reduce the value of your note and give the teacher a negative impression of your skills.