Differences in what varies and what is invariant make different things possible to learn.Consequently,the pattern of variation and invariance when dealing with some particular content is highly correlated with what the students learn about that content.For example,Marton and Pang(2006)found that in five comparable high-achieving secondary school classes,taught by five highly experienced teachers,the proportion of students who mastered a difficult economic concept varied between 6% and 97% depending on the different patterns of variation and invariance and on how systematically those patterns were used in the classrooms.In the next two sections I explore the effect of the systematic use of variation in classrooms by considering several examples.