Just as a thermostat adjusts room temperature, effective feedback helps maintain a supportive environment for learning. Because of the many factors affecting how recipients respond to feedback, research offers no simple prescription for making feedback work effectively. What works in one classroom for one teacher will not work for another teacher. Feedback given by a teacher to one student might motivate that student to strive harder to reach a goal, whereas exactly the same feedback given by the same teacher to another student might cause the student to give up. Although the existing research cannot provide teachers with a single "right" way to give feedback, it does suggest a number of important features that teachers can build into feedback that can increase the likelihood of a productive student response. The author has found that two principles seem to be almost universally applied in the classrooms where feedback is used to maximum effect. First, teachers must establish the classroom as a safe place for making mistakes. Second, and related to this, teachers who use feedback effectively convey the idea that smart is not something a person just is; it is something he or she can become. (Contains 1 figure.)