The aim of this study was to verify the relationship between type of school as a measure of socioeconomic conditions and caries prevalence among preschoolers and schoolchildren in Rio Claro, São Paulo State, Brazil, a city with fluoridated water supply. The data were secondary, from a sample of 888 children 5 to 12 years old enrolled in private and public schools. Caries was measured by the dmft and DMFT indices as well as the Care index. Qui-square and Mann-Whitney tests were utilized with 5% significance. In 5-year-old children, mean dmft was 2.50, and 42.20% were caries-free. At age 12, mean DMFT was 2.70 and 28.90% were caries-free. Caries prevalence rates in public schoolchildren as compared to private were 74.50% and 61.20%, respectively (p < 0.0001), and the dmft and DMFT scores were the highest in public schoolchildren (p < 0.05). The Care Index was higher in private schoolchildren (71.20%) as compared to public (52.80%). Highest caries rates were found among public schoolchildren, so the variable type of school proved sensitive for discriminating different oral health conditions; however limitations need to be recognized, suggesting that other variables should be assessed.