Bloom’s 2 Sigma Problem is an odd name for educational psychologist Benjamin Bloom’s discovery, first reported in 1984, that one-to-one tutoring isn’t just a little bit better than conventional classroom teaching:
Bloom found that the average student tutored one-to-one using mastery learning techniques performed two standard deviations better than students who learn via conventional instructional methods — that is, “the average tutored student was above 98% of the students in the control class”. Additionally, the variation of the students’ achievement changed: “about 90% of the tutored students… attained the level of summative achievement reached by only the highest 20%” of the control class.
The two-sigma part refers to average performance of ordinary students going up by two standard deviations when they received one-to-one tutoring and worked on material until they mastered it, and the problem part refers to the fact that such tutoring doesn’t come cheap.
My first reaction is surprise at the degree of the effect, but it should be obvious that advancing 30 students in lock-step means that many will be bored, a few will be in the sweet spot, and many will fall further and further behind, as the material builds on previous material they never learned.
So, my conclusion would be that conventional classroom teaching is largely a waste of time — but that’s not where educational experts place their emphasis:
Although much recent attention has focused on gaps in the achievement of different groups of students, the problem has been with us for decades. This paper presents the problem as one of reducing variation in students’ achievement, and reviews the work of renowned educator Benjamin Bloom on this problem. Bloom argued that to reduce variation in students’ achievement and to have all students learn well, we must increase variation in instructional approaches and learning time.
I suppose they see it as Bloom’s Paradox.
In his original paper, Bloom notes that a full-size classroom can get one-sigma results by switching to mastery learning, where students are tested not just for a final grade on a unit but to uncover where they need to do further corrective work, so they keep at it until they get it right.
It is odd, when you think about it, that we give students As, Bs, and Cs, and then advance them all to the next course, when they really should study the material until they earn a solid A before moving on — unless the goal of education isn’t conveying information but ranking students.