The State of Tennessee transitioned to new science standards. Previous methods for delivering professional development were unable to support teachers in pedagogy, content knowledge, or sustainability during this paradigm shift. As such, a lead teacher model was thoughtfully and intentionally implemented, and delivered professional development for three-dimensional learning and the Tennessee Academic Standards for Science. The lead teacher model provided for one middle school science lead teacher per grade level (6-8) per middle school, and one K-2 and one 3-5 STEM lead teacher per elementary school. The lead teachers participated in monthly professional learning communities, and then re-delivered that information to their schools and grade levels. Using a mixed methods design, the researcher examined the relationship between the effectiveness of lead teacher re-delivery sessions and student achievement of the group, self-efficacy, and how the current lead teacher model impacted self-reported science teaching practices. Research findings showed that as effectiveness scores of a lead teacher re-delivery session increased, so did student achievement. Analysis from a variety of qualitative instruments suggested the lead teacher model did impact teacher's self confidence in science knowledge and science teaching. Historical data provided unique themes for how the district's current lead teacher model impacted science teaching practices, and indicated suggestions for how to support teachers in the areas of science curriculum, assessment, and future professional development. Results from the research will provide district personnel with recommendations for how to enhance the lead teacher model during the continued transition to new science standards. [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.]