Carlisle, J. F., Correnti, R., Phelps, G., & Zeng, J., "Exploration of the contribution of teachers' knowledge about reading to their students' improvement in reading."
Reading and Writing: An Interdisciplinary Journal, 22, 459-486 (2009) includes evidence specifically related to the importance of secondary social studies knowledge.
In addition, research studies have demonstrated the positive impact of teacher content knowledge on student achievement. For example, see D. Goldhaber, "Everyone's Doing It, But What Does Teacher Testing Tell Us About Teacher Effectiveness?" Journal of Human Resources, vol. XLII no.4 (2007). Evidence can also be found in White, Presely, DeAngelis "Leveling up: Narrowing the teacher academic capital gap in Illinois," Illinois Education Research Council (2008); D. Goldhaber and D. Brewer, "Does teacher certification matter? High School Certification Status and Student Achievement." Educational Evaluation and Policy Analysis. 22: 129-145. (2000); and D. Goldhaber and D. Brewer, "Why Don't Schools and Teachers Seem to Matter? Assessing the impact of Unobservables on Educational Productivity." Journal of Human Resources (1998). See also Harris, D., and Sass, T., "Teacher Training, Teacher Quality and Student Achievement." Teacher Quality Research (2007).