This investigation is an exploratory study of the use of a metacognitive software tool in a social supportive learning environment. The tool combined metacognitive knowledge and regulation functionality embedded within the content of an eight week online graduate education course. Twenty-three learners, who were practicing teachers, used the tool. Prior knowledge of metacognition, including responses to the Metacognitive Awareness Inventory (Schraw & Dennison, 1994), was obtained. Prior knowledge of community instructional approaches was also obtained. Learner interviews focused on the mediational aspects of the metacognitive tool and the social supportive learning environment, as well as an evaluation of the tool. Content analysis, combined with an activity theory framework, was used to analyze data. Findings are organized around three main themes: prior knowledge, the usability of the tool from design and technical perspectives, and the effectiveness of the tool related to its design principles. The practicing teachers were found to be knowledgeable about metacognition and community; however, this knowledge did not often translate into successful instruction. Learners found the metacognitive tool easy to use, but had difficulty with its design for conversation. They found activity theory disconnections between the tool and other course tools, and found the other tools more successful at creating community. The tool was evaluated as equally useful for metacognitive knowledge and regulation, and more useful for more complex domain content than less complex content. Learners also found the tool useful for modeling the design of metacognitive instruction for their own teaching. Conclusions are offered for improvements to metacognitive instruction in general and in particular for the use of cognitive tools in a social supportive online learning environment. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]