Past research conducted by the National Academy of Sciences has shown that the inclusion of too much accelerated course content may be detrimental to the process of facilitating deeper conceptual learning in advanced high school classrooms. Researchers in this case study sought to compare three American high schools teaching AP U.S. Government courses, with two high schools adopting a PBL teaching approach, and the third acting as a control specimen. Results over two years revealed students of PBL classrooms to be performing at or above the average of students in traditionally taught classrooms, with students of PBL classrooms reporting a higher degree of confidence and preparedness upon examination.
Source: Boss, S., Johanson, C., Arnold, S. D., Parker, W. C., Nguyen, D., Mosborg, S., . . . Bransford, J. (2011). The Quest for Deeper Learning and Engagement in Advanced High School Courses. The Foundation Review, 3(3), 12-23. doi:10.4087/foundationreview-d-11-00007