Prior research across hundreds for introductory physics courses has demonstrated that traditional physics instruction does not generally lead to students learning physics concepts in a meaningful way, but that interactive-engagement physics courses do sometimes promote a great deal more student learning. In this work I analyze a reform effort in a large-enrollment, introductory, physics course. I find that evaluating a curriculum in isolation from other influences, such as the instructor implementation and the student population, is problematical. Instead, I propose a model of classroom culture identifying the curriculum, instructor, and student peer group as key components to creating a learning environment. Assessment, a key influence of classroom culture, is considered a product of the instructor/curriculum interaction. All three aspects of the classroom culture have the potential to influence student learning outcomes. I analyze the implementation of two different reformed physics series in terms of classroom culture. In a calculus-based course, I evaluate a new reform-based curriculum for the first and third quarters of instruction. In the first quarter, mechanics, I find that having an instructor teach in alignment with the philosophy of the reformed curriculum is essential, with students of only certain section instructors having improved outcomes over traditional instruction on measures of conceptual understanding. In the electromagnetism quarter of instruction, student outcomes for all reformed sections are higher than those from traditional sections in spite of variations in instructor implementation. The vast range of instructor-student interactions within such a reformed course are analyzed in an observational study, finding that some types of interactions are characteristic of particular instructors, regardless of the content studied that day. An analysis of assessment proposes an alternative grading method that is superior to the traditional grading practices, which are inadequate to consistently evaluate certain classes of test items. Those taking part in curriculum design or research in the context of physics classrooms must be aware that variations in instructor implementation, the student population, and assessment practices all have tremendous potential to influence student learning outcomes. [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.]