In this article, we compare conventional uses of metacognition with the kinds of metacognition required by the teaching profession. We discover that many of problems and tasks used in successful metacognitive interventions tend to be reasonably well-defined problems of limited duration, with known solutions. Teaching has unique qualities that differentiate it from many of the tasks and environments that metacognitive interventions have supported. Teachers often confront highly variable situations. This led us to believe that successful teaching can benefit from what we call adaptive metacognition, which involves change to oneself and to one's environment, in response to a wide range of classroom social and instructional variability. We present several examples to illustrate the nature of metacognition required by teachers and the challenges of helping teachers recognize situations that require adaptive metacognition. We conclude the article by describing an approach, critical event-based instruction, which we have recently developed to help teachers appreciate the need for metacognitive adaptation by seeing the novelty in everyday recurrent classroom events.