Interactive educational technologies, like intelligent tutoring systems, provide an excellent platform on which to perform research on metacognition. Such systems provide finegrained tracking and assessment of students’ cognitive and metacognitive behaviors. They also facilitate the implementation of tightly controlled experiments within the context of real classrooms. This chapter covers recent research on the impact of different types of metacognitive support in intelligent tutoring systems on both the learning of domain content and desired metacognitive behaviors. We describe results from four lines of controlled experimentation, mostly performed in the context of real classrooms, in vivo. Our results show clear benefits of metacognitive supports for domain content learning. We also demonstrate innovative methods for assessing real-time metacognitive behaviors as students are engaging in learning activities. Finally, we present some partial success in attempts to produce lasting improvements in metacognitive behaviors themselves and discuss why metacognitive behaviors may be resistant to change.