Some statisticians have pointed out that the field of statistics essentially exists to study the variability seen in everyday life. Because variability is so foundational, the "Guidelines for Assessment and Instruction in Statistics Education" (GAISE 2007), published by the American Statistical Association (ASA), recommend that teachers…

Several examples proved Van Hiele theory to be a useful ingredient in teaching of a summer course for high school students who had failed geometry during the school year are discussed. The theory provided a framework to help organize and reflect upon instruction for some key concepts in geometry.