This study investigated the impact of an inquiry-based science program on the critical thinking skills, science process skills, creativity, and science fair achievement of middle school students. Although research indicates the connection between inquiry and achievement, there is limited empirical research relating specific inquiry-based programs to critical thinking, creativity, and science fair achievement in middle school classrooms. The research took place in a small, suburban middle school in the northeast from November 2010 to May 2011. A sample of convenience was comprised of seventh and eighth grade students. The study was quasi-experimental in nature, with a pretest-posttest comparison group design using intact classrooms of students. Five instruments were administered related to the elements of science process skills, critical thinking, creative thinking, and science fair achievement. The scores of those students in the inquiry-based science program were compared to those students in the traditional science classroom to determine the impact of each method of delivering instruction. In the multivariate analysis of variance, the inquiry instruction group scored significantly higher for science process skills as measured by the Earthworm Test (p < 0.001) and Cognitive Integrity, an area of critical thinking measured by the CM3 (p < 0.025). In multiple regression analysis, program type contributed significantly to the prediction of science fair achievement scores above and beyond the predictor variables of science process skills, critical thinking, and creativity (p < 0.001). Science fair scores were significantly higher (p < 0.001) for the treatment as compared to that of the direct instruction group. Overall, science process skills (p < 0.025) and program type (p < 0.001) contributed significantly to the prediction of science fair 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/en-US/products/dissertations/individuals.shtml.]