Educators have recently come to consider inquiry based instruction as a more effective method of instruction than didactic instruction. Experience based learning theory suggests that student performance is linked to teaching method. However, research is limited on inquiry teaching and its effectiveness on preparing students to perform well on standardized tests. The purpose of the study to investigate whether one of these two teaching methodologies was more effective in increasing student performance on standardized science tests. The quasi experimental quantitative study was comprised of two stages. Stage 1 used a survey to identify teaching methods of a convenience sample of 57 teacher participants and determined level of inquiry used in instruction to place participants into instructional groups (the independent variable). Stage 2 used analysis of covariance (ANCOVA) to compare posttest scores on a standardized exam by teaching method. Additional analyses were conducted to examine the differences in science achievement by ethnicity, gender, and socioeconomic status by teaching methodology. Results demonstrated a statistically significant gain in test scores when taught using inquiry based instruction. Subpopulation analyses indicated all groups showed improved mean standardized test scores except African American students. The findings benefit teachers and students by presenting data supporting a method of content delivery that increases teacher efficacy and produces students with a greater cognition of science content that meets the school's mission and goals. [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.]