Are you referring to Blooms 2 sigma problem (https://en.m.wikipedia.org/wiki/Bloom%27s_2_sigma_problem https://en.m.wikipedia.org/wiki/Bloom%27s_2_sigma_problem

Are you referring to Blooms 2 sigma problem (https://en.m.wikipedia.org/wiki/Bloom%27s_2_sigma_problem https://en.m.wikipedia.org/wiki/Bloom%27s_2_sigma_problem)? While it did show that, that research was not done until the 80’s.