Research design
In the recitation / tutorial experiment, only one hour of instruction per week was modified.
Seven different faculty taught the classes — only one of them the researcher.
Two instructors taught twice— once with recitations and once with tutorials. In both cases the tutorial result was substantially better than the recitation result.
* E. F. Redish, J. M. Saul, and R. N. Steinberg, Am. J. Phys. 65, 45-54 (1997)