The Milwaukee sample involved four public schools. Two of the four were above average and the remaining two were
average in the Milwaukee metropolitan area. As in China, the U.S. schools were selected based on the recommendations of a group of mathematics supervisors in a school district and mathematics education professors in Milwaukee. These
schools were typical in the area in terms of the demographics of the student population and family background. After
the schools were chosen, one 6th-grade mathematics teacher from each of the four U.S. schools was selected from
those who had volunteered. All of the 6th-grade students taught by each of these selected teachers in each school were
included in the study giving a total of 232 U.S. students. A similar number of boys and girls were represented in both
the Guiyang sample