The purpose of this study was to investigate the impact of gender and type of inquiry curriculum (open or structured) on science process skills and epistemological beliefs in science of sixth grade students. The current study took place in an urban northeastern middle school. The researcher utilized a sample of convenience comprised of 303 sixth grade students taught by four science teachers on separate teams. The study employed mixed methods with a quasi-experimental design, pretest-posttest comparison group with 17 intact classrooms of students. Students' science process skills and epistemological beliefs in science (source, certainty, development, and justification) were measured before and after the intervention, which exposed different groups of students to different types of inquiry (structured or open). Differences between comparison and treatment groups and between male and female students were analyzed after the intervention, on science process skills, using a two-way analysis of covariance (ANCOVA), and, on epistemological beliefs in science, using a two-way multivariate analysis of covariance (MANCOVA). Responses from two focus groups of open inquiry students were cycle coded and examined for themes and patterns. Quantitative measurements indicated that girls scored significantly higher on science process skills than boys, regardless of type of inquiry instruction. Neither gender nor type of inquiry instruction predicted students' epistemological beliefs in science after accounting for students' pretest scores. The dimension Development accounted for 10.6% of the variance in students' science process skills. Qualitative results indicated that students with sophisticated epistemological beliefs expressed engagement with the open-inquiry curriculum. Students in both the sophisticated and naive beliefs groups identified challenges with the curriculum and improvement in learning as major themes. The types of challenges identified differed between the groups: sophisticated beliefs group students focused on their insecurity of not knowing how to complete the activities correctly, and naive beliefs group students focused on the amount of work and how long it took them to complete it. The description of the improvement in learning was at a basic level for the naive beliefs group and at a more complex level for the sophisticated beliefs group. Implications for researchers and educators are discussed. [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.]