they could generate an upward bias in the elasticity of earnings with respect to work city size (when observed working in big cities with average or below average wages). Taken together, these two insights explain our finding of a larger elasticity of wages with respect to college than work city.

This finding highlights the importance of our pre-labor market locational data. Administrative datasets usually follow an individual from the beginning of her work life and use repeated observations per individual to handle the inherent self-selection into the work city, with identification of (work city) agglomeration effects being driven by migrants (Combes, Duranton, and Gobillon, 2008, D’Costa and Overman, 2014, De la Roca and Puga, 2017). In contrast, our pre-labor market locational data enable us to examine the spatial trajectory leading individuals to their work city, thereby underscoring at what point of this trajectory a large city pays off the most.

# **4. Summary and conclusions**

Our study examines the dynamic sorting that leads to differences in skills across cities of different sizes, and the consequences of this pre-labor market sorting on estimated agglomeration effects. We find an elasticity of wages with respect to city population of 0.052, in line with the previous literature. In addition, we find a substantial effect on wages for college city size; this effect is much larger than that of high school or work city size. We also document substantial returns to mobility, particularly with moves to attend college in big cities.

Turning to the determinants of pre-labor market sorting, particularly with respect to the choice to move for college, we find that ability (as proxied through Saber 11, a national high school exit exam) is not a key determinant for mobility in Colombia. Instead, we find that access to college opportunities and household income are major drivers of pre-labor market sorting. Individuals from small cities also perceive a value in moving for college that goes beyond mere access to college, as those from small cities are disproportionately more likely to move for college.

We show the economic consequences of this pre-labor market sorting in terms of worker earnings by city size. In line with our hypothesis, in the big cities the highest wages are for those who moved there for college and stayed in that city for work. In the small and medium cities, the highest wage earners are workers who moved there for work having attended college in a larger city. These workers are on average less able compared to those who work in big cities, but are relatively more able than the ones who never moved from small cities and, thus, are the highest earners in the small cities. This last finding is suggestive of a comparative advantage story: the most able migrants attain labor market success in the big city, while the relatively less able who attended college in the big city move to a small city for work, where they are the highest earners.

Altogether, our findings illustrate the dynamic sorting of skilled workers prior to labor market entry in a developing country setting, with the most talented sorting to big cities as a result of being there for high school or of attending college there. Our study also highlights the role of luck. Those born in big cities such as Bogota, or who happen to be in a big city for high school, do not have to move to access college, while those who spent their youth in small cities with limited access to public colleges have to move if they want to attain a college degree. More important, 29