# **1 Introduction**

The average child in a low-income country is expected to attend 5.6 fewer years of school than a child in a high-income country (World Bank, 2020).<sup>1</sup> By the age of 10, 90 percent of children in low-income countries still cannot read with comprehension, compared with only 9 percent in high-income countries (Azevedo et al., 2021). With limited resources, policymakers must make tough choices about what to invest in to improve education outcomes—–from constructing schools to coaching teachers, from improving school management to deploying new educational software. Making these investment decisions requires comparable data on both the benefits and costs—–i.e., the cost-effectiveness—–of alternative approaches.

However, the impacts of educational interventions are often reported in ways that make these comparisons difficult. For example, policymakers must choose between interventions that increase the number of years a child stays in school and investments that deliver increased learning during those years, without a good way of comparing progress against these alternative outcomes. But policymakers want a combination of the two. Politicians like Boris Johnson and advocates like Malala have called for an increase in the number of “years of quality education,” a single concept that incorporates both quality and quantity dimensions (Crawfurd, Evans, Hares, & Moscoviz, 2020; McKeever, 2020). There is evidence that some of the benefits of education, including economic growth, are more closely associated with learning (Hanushek & Woessmann, 2012), whereas others are associated with years of schooling (Baird, McIntosh, & Ozler<sup> ̈</sup> , 2011; De Neve, Fink, Subramanian, Moyo, & Bor, 2015; Duflo, Dupas, & Kremer, 2021). These two dimensions of education cannot be considered entirely separately. Improving the quality of education has more impact if more children go to school for longer, and programs that increase years of schooling lead to more learning if the underlying education system is of a higher quality.

In this paper, we analyze over 150 educational policies and interventions across 46 countries and identify the most efficient policies and interventions to improve education outcomes. We use a recently developed, unified measure—learning-adjusted years of schooling (LAYS)—that combines improvements in access and quality. By doing so, we make it possible to compare the effectiveness of a broad range of education interventions using a concrete and policy-salient metric.<sup>2</sup><sup>_,_3</sup> For a subset of interventions for which cost data are available, we include cost-effectiveness analysis and comparisons, a critical component to assess trade-offs of the most efficient policy and program to invest in.

> 1We calculate this based on a measure of expected years of schooling using source data from the UNESCO Institute for Statistics (UIS) compiled for the World Bank Human Capital Index 2020.

> 2In previous work, the concept of LAYS has been applied to characterizing the differences in quantity and quality of education across countries (Filmer, Rogers, Angrist, & Sabarwal, 2020), which we refer to in this study as “macro-LAYS” to distinguish them from intervention- and policy-level effects expressed in terms of LAYS, which we refer to as “micro-LAYS.”

> 3Since we adjust any increase in years of schooling for quality, one implication is that in the combined measure, improved access is valued in large part to the extent that schooling leads to at least some improvements in learning. This reflects an explicit value judgement that a central goal of schooling is to produce learning, and that other benefits of schooling (such as enhanced socio-emotional skills and reduced fertility) are not the only ones to take into account.

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