As educational accountability pressures and science teacher attrition rates within American public-school systems continue to rise, so does the need for improved reform-based professional development (PD) opportunities that allow science educators to challenge their pedagogical beliefs and teaching practices. This qualitative case study explores the relationships between three secondary science teachers' beliefs about instruction, assessment, and instructional practice to support future PD design models. This study uses various data gathering and analysis tools to triangulate teachers' beliefs and instruction data to support their holistic alignment to one of three domains within an assessment continuum framework. The results show inconsistencies in science teachers' pedagogical knowledge and beliefs about learning and assessment relative to their instructional practices. The teachers' beliefs about science inquiry and what is or is not important for students learning science aligned with some of the teacher's observed lessons and artifacts, although it was not a consistent theme among the participants. This study's results contribute to the existing body of research demonstrating that teachers' knowledge and beliefs do not consistently translate into their instruction and assessment practices. Educational reformers can use this study's processes and data to develop reform-based PD opportunities that encourage reflection, such as Cognitive Coaching and Professional Learning Communities. These reflective PD models can challenge and change existing pedagogical beliefs and instructional practices while encouraging professional growth to keep science teachers in the profession and improve students' academic achievement. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]