Many students reach the middle school level without appropriate critical thinking skills. This has important implications for educators and the future workforce. This mixed methods quasi-experimental design study investigated the use of a science inquiry kit and its effect on the critical thinking skills and dispositions of elementary students. Third grade students and their six teachers were the participants in this study. Two instruments were used to evaluate students' critical thinking skills and dispositions. Post-test results for critical thinking skills indicated the comparison group had increased their means significantly. Evaluation of the treatment groups pre-test vs. post-test means indicated that there was a significant difference; although it was not as great as the difference between the comparison group's pre-test vs. post-test means. The instrument used to evaluate the students' critical disposition did not show a significant difference between the post-test means. The qualitative portion was conducted to discover the experiences, training, and pedagogy used to teach science inquiry and critical thinking skills. The data revealed that teachers had very limited experiences with training in either science inquiry or critical thinking skills; their pedagogy in both areas was also fairly limited. The teachers in the treatment group expressed that they were pleased with the use of the kit in regard to its influence on their students' content knowledge and critical thinking skills, and they felt that the students' critical thinking skills improved as a result of using the science inquiry kit. Recommendations include repeating the use of the science kit with other third grade classes and with older students to discover if similar results are obtained. Additional information should be obtained from other teachers regarding their training in science inquiry and critical thinking skills to determine if this is a local issue or if it is a pervasive theme. [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.]