These are especially effective with non-verbal children. It keeps the communication open between parent and teacher. Plus, sometimes writing to a teacher makes it easier to communicate an idea in the way that you want to express it. A stressed child cannot attend to task, often exhibits disruptive behavior, or may simply space out. Teachers may misread the signs.
Examples range from divorce to a sick grandmother to a new baby.
Each student has a very different response to these life changes. In order to get your point across or convince people to try something they might not be inclined to do, be positive and enthusiastic. Be very upfront and give them factual information about your child's needs to alleviate their fears. Explain the reasons you want something done, then suggest ways to do it. You never know what will work.