SAXE, GEOFFREY B. The Mathematics of Child Street Vendors. CHILD DEVELOPMENT, 1988, 59, 14151425. The mathematical understandings of 23 10-12-year-old candy sellers with little or no schooling from Brazil's northeast were compared to 2 groups of nonvendors matched for age and schooling-a group from the same urban setting and a group from a nearby rural setting. Children's performances were analyzed on 3 types of mathematical problems: representation of large numerical values, arithmetical operations on currency values, and ratio comparisons. Vendors and nonvendors alike had developed nonstandard means to represent large numerical values, an expected result since problems involving large values emerge in the everyday activities of each population group. Most vendors, in contrast to nonvendors, had developed adequate strategies to solve arithmetical and ratio problems involving large numerical values, also an expected finding since these problem types emerge frequently only in the everyday activities of the vendor population. The findings are interpreted as supporting a model of cognitive development in which children construct novel understandings as they address problems that emerge in their everyday cultural practices.