Inclusion Criteria:  Willingness of parents to give consent Membership in randomly-selected classes at the selected schools.  Exclusion Criteria:  Children without consent from their parents will be excluded. Children having myopia (myopic spherical equivalent refractive error of <= -0.5D in one or both eyes) at baseline are excluded from the primary analysis, although they will be included in the secondary analyses, so there will be no need to exclude them from continuing to study with their classmates and use the assigned classroom.