This paper proposes a new measure of social mobility. It is based on schooling gap regressions, and uses the Fields decomposition to determine the importance of family background in explaining teenagers’ schooling gaps. The method is applied to a sample of 18 Latin American household surveys conducted in the late 1990s. We find Chile, Argentina, Uruguay, and Peru among the countries with highest social mobility, and Guatemala and Brazil among the least socially mobile countries. The results show that social mobility is positively correlated with GDP and general educational attainment, but not related to income inequality in any obvious way. Social mobility is generally higher in highly urbanized countries. The schooling gap regressions also reveal differences in opportunities within the family. Resources are clearly being diverted away from older siblings (especially sisters) towards younger siblings. In addition, it is an advantage to be born into the household relatively late in the lifecycle of the parents. For most countries, female teenagers were found to have significantly smaller schooling gaps than male teenagers. This did not make them significantly more mobile, however.