Does early tracking affect learning inequalities? Revisiting difference-in-differences modeling strategies with international assessments

The development of international surveys on children’s learning like PISA, PIRLS and TIMSS—delivering comparable achievement measures across educational systems— has revealed large cross-country variability in average performance and in the degree of inequality across social groups. A key question is whether and how institutional diferences afect the level and distribution of educational outcomes. In this contribution, we discuss the diference-in-diferences strategies employed in the existing literature to evaluate the efect of early tracking on learning inequalities exploiting international assessments administered at diferent age/grades. In their seminal paper, Hanushek and Woessmann (Econ J 116:C63–C76, 2006) analyze with two-step estimation the efect of early tracking on overall inequalities, measured by test scores’ variability indexes. Later work of other scholars in the economics and sociology of education focuses instead on inequalities among children of diferent family background, using individual-level models on pooled data from diferent countries and assessments. In this contribution, we show that individual pooled diference-in-diferences models are quite restrictive and that in essence they estimate the efect of tracking by double diferentiating the estimated cross-sectional family background regression coefcients between tracking regimes and learning assessments. Starting from a simple learning growth model, we show that if test scores at diferent surveys are not measured on the same scale, as occurs for international learning assessments, pooled individual models may deliver severely biased results. Instead, the scaling problem does not afect the two-step approach. For this reason, we suggest using two-step estimation also to analyze family-background achievement inequalities. Against this background, using PIRLS-2006 and PISA-2012 we conduct two-step analyses, fnding new evidence that early tracking fosters both overall inequalities and family background differentials in reading literacy.