Although the National Association for Gifted Children states that gifted and talented students from prekindergarten through high school require a differentiated curriculum in all subject areas to maximize their abilities, few gifted programs focus on developing the abilities of high school students in the domain of social studies. Further, the few studies that have focused on examining curriculum models designed to challenge high ability students in social studies have not proven efficacious in increasing student achievement in social studies. The current study was designed to investigate whether a differentiated curriculum based on the development of historical expertise that was taught using the cognitive apprenticeship instructional model is a useful framework for challenging gifted and talented high school students and enhancing their achievement. Seven matched pairs of gifted and talented ninth graders who were enrolled in an honors world history course volunteered and participated in the current study. Participants comprised either a treatment group or a comparison group and wrote a document-based historical essay. Essays were scored by trained raters who used a rubric to assess the overall quality of the essay as well as five components of interest: position taking, use of documents, document interpretation, awareness of multiple perspectives, and understanding and analysis of bias. Analysis of the scores using the Wilcoxon Matched Pairs Signed Ranks test found that students in the treatment group produced essays that were scored higher than their comparison-group counterparts. Statistically significant differences demonstrating treatment efficacy were also found in three of the five components of interest. In each case, the treatment was found to have a medium to large effect on student outcomes. The results of the study support the use of domain-based expertise as a viable framework for designing curricula to challenge gifted and talented high school learners. The study also affirms the efficacy of the cognitive apprenticeship instructional model as a vehicle for developing expert-like performance in students. The study highlights the Innovation Configuration Map as a method for measuring fidelity of treatment implementation and mitigating threats to validity in research studies. [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.]