Martin Seligman is a Professor of Positive Psychology. He describes in his book "Authentic Happiness" how he organises Gratitude Evenings to teach the tremendous power of gratitude to his students. He asks each student to bring a guest – someone who has been very important in their lives but whom they have never properly thanked. The student writes an account of what this person means to them and reads it aloud at the evening. Apparently these evenings are the high point of the course.
Seligman, M.E.P. (2003). Authentic Happiness: Using the New Positive Psychology to Realize Your Potential for Lasting Fulfilment. London: Nicholas Brealey Publishing.