Investigating the nature of our conceptualizations of learning is a crucial step towards reducing the research-to-practice gap and developing strategies toward adoption of powerful practices in teaching and learning based on educational and Learning Sciences research. The purpose of this study was to develop robust characterizations of the conceptualizations of learning among a group of learning scientists and a comparison group of professors in STEM fields. This study described differences between conceptualizations of learning and related beliefs regarding educational practices. Analysis using the Iceberg Framework for Conceptualization Analysis found two conceptualizations of learning. In the "Transfer/Acquisition" conceptualization of learning experiences, analogies, and surface metaphors interact over time leading to the emergence of an "Acquisition and Object Manipulation" conceptual metaphor and an "Object Possession" conceptual story, which interact with an "Individualist/Competition" worldview and a "Positivist/Post-Positivist" paradigm. Practices aligned with this conceptualization include exams, grading, student-teacher interaction, cooperative learning, textbooks, clickers, and lectures. The "Construction/Becoming" conceptualization of learning involves interactions between elements including a "Construction, Becoming, and Apprenticeship" conceptual metaphor, a "Situated Becoming" conceptual story, a "Collaborative/Cooperative" worldview, and an "Interpretivist/ Constructivist" paradigm from which practices emerge including interest-based learning, learner agency, real-world impact work, participation in a community of practice, collaboration, reflection, self-evaluation, making and design work. Comparative case study analysis found that the Construction/Becoming conceptualization of learning was dominant in the Learning Sciences group and the Transfer/Acquisition conceptualization was dominant in the STEM Professors group. The "high-impact" practices from the literature were more associated with the Construction/Becoming conceptualization, and the practices the literature suggests should be minimized were most associated with the Transfer/Acquisition conceptualization. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]