extra year of primary schooling is associated with larger learning gains in Viet Nam compared to other developing countries.<sup>2</sup> More broadly, large increases in educational enrollment in many developing countries have been associated with stagnant or even declining learning achievements by level of education (Pritchett, 2013; Le Nestour et al., 2023), highlighting the challenges brought by rapid educational expansions. Several studies argue that when quality differences are incorporated in the measurement of human capital, its contribution in accounting for cross-country income gaps can be substantially larger (see for example Schoellman, 2012; Angrist et al., 2021b).

Figure III: Average Learning Score and Development <!-- Start of picture text --> (a) Primary (b) Secondary<br>600 600<br>SGP<br>500400300 BDICODMWINERLBRMOZ MDGBFAETHSLEHTITGOTCDUGAMLIRWAGINGMBTZAYEMNPLZWECOMSENBEN ZMB TJKCMRLSOKHMKEN BGD SDNMRTCIVPAKCOGMMRKGZHNDNICGHANGABLZLAOPHL MDA SLVMAR GTM AGOJAMSWZIDNJORIRQNAM GUY ECUPERPRYEGYGEOZAFIRNCOLMKDAZEBRADOMBWAGABCRIBGRMEXMUSURYARG ROU HRVCHLKAZSYCLVAPANHUNRUSTURGRCLTUPOLSVK CYP PRTTTOSVNCZEMLTOMNESPITANZLISRFRAFINTWNCANISLDNKDEUBHRAUSAUTSWEHKGNLDSAUKWTUSA NORAREIRLLUX MACQAT 550500450400 VENINDVNM MDA IDNJORTUNALBPERDZAGEOCHNCOLMKDAZEBRADOMLBNSRBTHACRIBGRMNEMEX MUS URYARG ROU HRVCHLMYSKAZLVAPANHUN RUS TURGRC LTU POLSVKESTPRTTTOSVNCZEMLT ESP ITANZLISRKORJPNFRAFINGBRBELTWNCANISLDNKDEUAUSAUTSWEHKGNLD USA NOR CHEARESGPIRLLUX MACQAT<br>200 350 KGZ<br>7 8 9 10 11 12 8 9 10 11 12<br>Log GDP per worker in PPP (2015) Log GDP per worker in PPP (2015)<br>Average Learning Score Average Learning Score<br><!-- End of picture text --> _Notes_ : The figure plots the average learning score for primary (left panel) and secondary school (right panel) students from the Harmonized Learning Outcomes Database (Angrist et al., 2021a) against log GDP per worker (in PPP terms) in 2015. The learning score is averaged across all available subjects and years. GDP per worker is taken from version 9.0 of the Penn World Tables (Feenstra et al., 2015).

**These results underline the need for effective investments making schools in poor countries well-equipped to deliver learning against the backdrop of a rapidly growing student population** . The existing literature highlights a number of promising margins. Based on a comprehensive review of the evidence, the Global Education Evidence Advisory Panel (2023) concludes that improving classroom instruction through structured pedagogy and targeted support for students falling behind, and the provision of information on education quality are particularly cost-effective interventions. In many developing countries, it has been documented that teachers perform poorly in terms of both subject knowledge and exerted effort (Bold et al., 2017); in light of this, the returns to policies that train teachers and provide them with appropriate incentives are likely to be high (Kremer et al., 2013; Evans and Popova, 2016). New technologies could help by both complementing teachers’ efforts and accommodating a growing and increasingly diverse student population; for example, Muralidharan et al. (2019) reports large performance gains associated with an instruction program that dynamically adapts the proposed content to the learning level of each student. More broadly, systemic reforms are

> 2Indirect evidence on the crucial role of school quality for human capital formation comes from the learning losses experienced by several countries during the pandemic, which were large and highly heterogeneous across countries (Hanushek and Strauss, 2024).

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