We all know Dr. Benjamin Bloom for his taxonomy but did you know that he also wrote about how learning occurs under different methods of instruction? Using research conducted by two of his doctoral students (which he guided), the 2 Sigma Problem emerged. The instructional methods were identified as conventional, mastery and tutoring. Although written in 1984, I am struck by the lack of movement from the conventional teaching method although active teaching leading to active learning has made an impact and continues to grow as practitioners discover news ways to ignite student performance. Of course we are left wondering which mode worked the best? Bloom, Anania, and Burke found that using the conventional mode of instruction as a baseline, students under mastery learning saw a one-sigma (standard deviation) improvement in performance. Students who received one-on-one tutoring saw a two-sigma improvement. As Alfred Essa, Vice President of R&D and Analytics at McGraw-Hill Education, explains "A one sigma is roughly a one-letter grade in improvement. It can be the difference between a student failing a course and passing a course—and most educational interventions don’t come close. If one sigma of improvement is huge, two is monumental." You can read Bloom's article here.