Metacognition is widely studied for its influence on the effectiveness of learning. With Exploratory Computer-Based Learning Environments (ECBLE), metacognition is found to be especially important because these environments require adaptive metacognitive control by the learners due to their open-ended structure that allows for multiple learning paths. Although researchers recognize the importance of metacognitive processes when learning with ECBLE, there is a small number of studies that systematically investigated the metacognitive processes. This dissertation addressed the problem by developing and validating a method, the Behavioral Measure of Metacognitive Processes (BMMP), to examine metacognitive processes. The first study established the construct validity and reliability of the BMMP through triangulation with the verbal learning process data from think-aloud protocol. The second study applied the BMMP to examine the predictive validity of the methods while studying the effects of learners' prior knowledge, interest, and self-efficacy on their metacognitive processes and learning outcome. The predictive validity was established by demonstrating the ability of the BMMP measures to predict the learning outcome. While learners' cognitive and motivational characteristics did not predict how well learners metacognitively controlled their learning process, all learners benefited with better learning outcome when they exercised more adaptive metacognitive control during learning. Also, learners' perceived cognitive load predicted the learning outcome. The third study further examined the predictive validity of the BMMP by studying whether procedural scaffolds can benefit learners with more adaptive metacognitive control and subsequent learning. A worksheet was used as scaffold to assist learners through the steps of scientific inquiry. While most subjects demonstrated adaptive metacognitive control, the learning outcome depended on their prior knowledge and mastery goal-orientation. Also, subjects with high mastery goal-orientation were more likely to demonstrate selective use of the scaffold. The BMMP reliably provided means to examine when, why, and for whom learning with ECBLE can be effective. The BMMP can also be used with other examples of ECBLE, such as games. However, given the known limitations of the behavioral data, triangulation with other data sources, such as verbal data, is recommended for future research. [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.]