Bloom's 2 Sigma Problem

Bloom's 2 sigma problem is the educational phenomenon that the average student tutored one to one using mastery learning techniques performed two standard deviations better than students taught in an ordinary classroom. It was reported in 1984 by the educational psychologist Benjamin Bloom in the journal Educational Researcher, drawing on the dissertation results of University of Chicago doctoral students Joanne Anania and Joseph Arthur Burke; Bloom found that the average tutored student scored above 98 percent of students in the control classroom, and that about 90 percent of tutored students reached the level of achievement reached by only the top 20 percent of the control group. Bloom framed the associated problem as finding methods of group instruction as effective as one to one tutoring, and the finding has since been used to show that factors outside a teacher's control shape student outcomes, motivating research into alternative teaching methods and developments such as cognitive tutors and learning management systems.