The purpose of this action research study was to explore the impact of problem-based learning on science instruction in my eighth-grade college preparatory classroom. Constructivism was the framework for this study. Problem-based learning is based on constructivist principles, and it served as the instructional model for this study. PBL can foster the use of problem-solving skills, critical thinking skills, and communication skills, which are needed in the 21st century. This research study was centered around three research questions. The first question asked about the impact PBL has on students' science achievement. The second question asked how does PBL impact students' engagement towards science and learning. The third question asked how does PBL impact students' problem-solving skills. This research study utilized a mixed-methods design. Quantitative and qualitative data showed that although some students struggled with abstract scientific concepts, PBL increased students' academic achievement in science. Data also showed that while students may need frequent redirection, the activities utilized while implementing PBL engaged most students. I also found that although students may need additional support, PBL improved students' problem-solving skills. An action plan was created to implement PBL school-wide. Implications for classroom practice and future research were also 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.]