This quantitative research examined the effect of the implementation of project-based learning and assessment on the standardized test scores of high school students. Data were collected through a quantitative approach using standardized test scores for ninth-grade students taking the end-of-course World History and Geography to 1500 A.D. (C.E.) assessment developed by the Virginia Department of Education and based on the Virginia Standards of Learning. The researcher used a causal-comparative quantitative research design and an independent t test to compare the mean scores on the end-of-course standardized test of two independent groups of world history students. The findings presented can lead students, educators, community members, and policymakers to improve learning outcomes for history students and improve the practical attainment of 21st-century skills. Suggestions for additional research and implications for implementing project-based learning and assessment in curricula are detailed. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]