This paper uses longitudinal data from seven countries to assess how systems of educational tracking can impact on social mobility. Studies which simply compare comprehensive and tracked systems may be flawed, the research suggests, because of differences in how countries separate students for instructional purposes. The researchers used large-scale longitudinal data from Denmark, England, Finland, France, Germany, Israel, and Italy, most of it relating to children born in the 1970s. They asked three questions: to what extent can social origins predict the type of secondary school track a child attends; to what extent can the track followed in secondary school predict educational and work outcomes; and to what extent does tracking in secondary education account for the long-term effects of social origin? The research finds that Germany, where selection takes place early, has the most pronounced association between origins and destinations, while Nordic countries which favour inclusivity show the weakest associations. But when country-specific factors are taken into account the role of tracking in mediating social reproduction remains remarkably similar across all countries. The paper concludes that future studies need to factor in fine-grained, rather than crude, differences in countries’ systems of educational differentiation when studying links between systems, social origins and outcomes.