As part of the video study, an independent group of American college mathematics teachers was asked to evaluate the quality of mathematical content in a representative sub-sample of the video lessons. They examined 30 lessons in each country, basing their judgments on a detailed written description of each lesson’s content. Descriptions were altered to disguise the country of origin (deleting, for example, references to currency that might give the country away). This was done to decrease the likelihood that judgments would be biased by knowing the country from which each lesson came.

This group completed a number of in-depth analyses, the simplest of which involved making global judgments of the quality of each lesson’s content on a three-point scale (Low, Medium, High). Their judgments are summarized in the graph. Whereas 39 percent of the Japanese lessons and 28 percent of the German lessons received the highest rating, none of theUS lessons received the highest rating. Eighty-nine percent of US lessons received the lowest rating, compared with 11 percent of Japanese lessons.