Bloom's 2 Sigma Problem

Bloom's 2 sigma problem is the educational psychologist Benjamin Bloom's 1984 finding, published in the journal Educational Researcher, that the average student who received one-to-one tutoring using mastery learning methods performed two standard deviations better than students taught the same material in an ordinary classroom, a gap large enough that the average tutored student scored above 98 percent of students in the untutored control group. Drawing on dissertation research by the University of Chicago graduate students Joanne Anania and Joseph Arthur Burke, Bloom also reported that roughly 90 percent of tutored students reached an achievement level that only the top 20 percent of the control classroom reached. He framed the resulting challenge, since one-to-one tutoring for every student is not practical at scale, as the problem of finding a method of group instruction that could produce results as strong as individual tutoring does, a problem later researchers have pursued through approaches including cognitive tutoring software and learning management systems, some of which have reported gains larger than Bloom's own findings.