The purpose of this study was to examine influences of standards-based reform and high-stakes testing on teacher practices and perceptions in high school science classrooms. A literature review suggested that teacher practices and perceptions are affected by emphasis on standards-based reform and high-stakes testing and that state level implementation of national accountability requirements and experiences of individual teachers vary. The central research question addressed the effects of national, state, and local emphasis on high-stakes test scores on high school science teachers' practices and perceptions in one suburban school district. A mixed methods study utilizing a single-stage, cross-sectional survey, which included closed and open-ended items, was distributed to two subgroups of science educators. The first subgroup included teachers whose students take a high-stakes test at the end of the course and the second included teachers whose students do not have to take such a test. Quantitative responses were coded and independent measures t tests used for data analysis. Qualitative data were analyzed in accordance with the phenomenological tradition. Findings indicated that most teachers reported their practices were affected by the pressures of testing and that, in practice, the subgroups were largely similar. Differences between subgroups included the use of problem-solving strategies and the influences of professional development. The data collected indicated some teachers lack a clear understanding of national science standards and some would benefit from professional learning related to student-centered practices. This study promoted social change by encouraging teachers to engage in ongoing inquiry which is necessary to advance practices that will prepare students to succeed academically. [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/en-US/products/dissertations/individuals.shtml.]