In the early 1980s, in a series of randomly controlled trials in a variety of high school courses, he found that students who received one-on-one tutoring performed two standard deviations better than students in a classroom course. In other words, the average student in the tutoring program was better than approximately 98% of the students in the classroom course. Delving deeper, 90% of the students in the tutoring program were in the top 20% of the students in the control classroom course.
This result is not surprising if you take a broad and deep look at education. In the fitness world, personal trainers have never been more demanded. Life coaches, corporate mentors, executive coaches and related fields have multiplied. Some theorize that holistic medicine practitioners have prospered because they spend much more time, one-on-one, with their patients than traditional doctors. SAT preparation instructors, quality free material on the web notwithstanding, have never commanded higher prices.
Deeper, one-on-one education is the history of education. The master-apprentice model has endured for thousands of years. Most royalty throughout history were tutored. (Interestingly, many of their tutors were famous philosophers, like Aristotle tutoring Alexander the Great, and Rene Descartes tutoring the Queen of Sweden.)
Bloom called his finding the two sigma “problem” because he thought one-on-one instruction would be too expensive to implement on a wide scale; he was issuing a challenge to researchers to find ways of teaching that were as effective as one-on-one instruction.
Sadly, he did not try to polish his silver bullet. His tutors were not completely green; they were trained in “mastery learning” techniques. But what kind of effect would truly awesome tutors, who are widespread throughout the private sector, have? And what discoveries could they provide classroom teachers?