Do child laborers learn less?

Child labor is frowned upon because going to school is deemed essential to the development of every child, especially in terms of giving her the essential tools to do well as an adult. It is generally recognized that parents do not want to keep their child away from school (excluding those who insist on home schooling), but that sometimes economic hardship forces them to have children help with current expenses to the detriment of their future earnings. But child labor is not a black and white outcome. It may happen that children work and go to school. To what extend does this have an impact of academic outcomes?

Patrick Emerson, Vladimir Ponczek and André Portela Souza got their hands on excellent data from the municipal schools in São Paulo, where they can track students across several years, know whether they work outside the home, what their study habits are as well as a few socio-economic characteristics of the family. They find that transitioning into child labor leads to a decline in test scores for mathematics and Portuguese in the order of 6% to 10% of a standard deviation. That may not look like much, but this adds up to a quarter to a full year of education by the time they are done with school. However, one may argue that they also learn some useful skills for the labor market while working, so one can wonder how it look like in terms of adult outcomes.