english: The mastery-based population was a full standard deviation, or sigma, in achievement scores better than the standard lecture-based class, and the individual tutoring gives you 2 sigma improvement in performance.
non_english: De meesterschapsgroep was een volle standaarddeviatie, of sigma, beter qua prestatiescore dan de groep die les kreeg in de klas, en één-op-één-lessen gaven 2 sigma verbetering qua prestaties.