| Purpose. The purpose of this grounded theory study was to refine, using a Delphi study process, the four categories of the theoretical model of the comprehensive knowledge base required by providers of professional development for K-12 teachers of science generated from a review of the literature.;Methodology. This grounded theory study used data collected through a modified Delphi technique and interviews to refine and validate the literature-based knowledge base required by providers of professional development for K-12 teachers of science. Twenty-three participants, experts in the fields of science education, how people learn, instructional and assessment strategies, and learning contexts, responded to the study's questions.;Findings. By "densifying" the four categories of the knowledge base, this study determined the causal conditions (the science subject matter knowledge), the intervening conditions (how people learn), the strategies (the effective instructional and assessment strategies), and the context (the context and culture of formal learning environments) surrounding the science professional development process. Eight sections were added to the literature-based knowledge base; the final model comprised of forty-nine sections. The average length of the operational definitions increased nearly threefold and the number of citations per operational definition increased more than twofold.;Conclusions. A four-category comprehensive model that can serve as the foundation for the knowledge base required by science professional developers now exists. Subject matter knowledge includes science concepts, inquiry, the nature of science, and scientific habits of mind; how people learn includes the principles of learning, active learning, andragogy, variations in learners, neuroscience and cognitive science, and change theory; effective instructional and assessment strategies include constructivist learning and inquiry-based teaching, differentiation of instruction, making knowledge and thinking accessible to learners, automatic and fluent retrieval of nonscience-specific skills, and science assessment and assessment strategies, science-specific instructional strategies, and safety within a learning environment; and, contextual knowledge includes curriculum selection and implementation strategies and knowledge of building program coherence.;Recommendations. Further research on the use of which specific instructional strategies identified in the refined knowledge base have positive, significant effect sizes for adult learners is recommended. |
