Results from the 2015 Program for International Student Assessment found that children who attend preschool between the ages of three and five scored higher on math as teens. Even after taking into account socioeconomic status, students who had attended at least a year of preschool were still less likely to be low performers in math on PISA than those who had not. Some U.S. experts warn, however, that international comparisons are difficult because of varied approaches to preschool and test administration. (Education Week)