# 1. Introduction

The past 25 years have witnessed an unprecedented educational expansion in developing countries. Most children in the world now have access to school. By 2015, enrollment in primary education in low‐income countries reached 80 percent, compared to 42 percent in 1990 (World Bank 2017).<sup>2</sup> Children also stay in school longer. Average years of schooling among adults almost doubled, from 3.9 years in 1980 to 7.5 years in 2010 (Lee and Lee 2016). However, increased schooling does not automatically translate into better learning outcomes for all children. In many places in Africa, Latin American, and South Asia, students who have completed primary education still cannot read or add two‐digit numbers (Majgaard and Mingat 2012; Dundar et al. 2014; Pritchett, Banerji, and Kenny 2013). Even in middle‐income countries, students learn much less than their peers in rich countries (World Bank 2018). The Programme for International Student Assessment (PISA) 2015 survey shows that the 15‐year‐old top performers (above the 75<sup>th</sup> percentile) in mathematics in the Dominican Republic, Algeria, Kosovo and Tunisia scored lower than those at the 25<sup>th</sup> percentile of the OECD average (Figure 1) (OECD 2016). Other international assessments show similar trends (Mullis et al. 2016; PASEC 2015; Pizarro et al. 2016).

Governments are searching for more innovative and effective ways to improve learning. This not only translates into ongoing efforts to try new education interventions, but also increased use of experimental or quasi‐experimental methods to measure the impacts of these interventions. By 2016, there were more than 350 impact evaluation studies with learning outcomes from low‐ and middle‐income countries; in 2000, there were only about 32 (Evans and Popova 2016; World Bank 2018). Indeed, there is a wide range of possible education interventions, from providing school meals to students to offering cash transfers conditional on school attendance; from giving free learning materials to students to training teachers in new instructional techniques; from constructing new schools to strengthening school management; and from increasing parental engagement to promoting community‐based monitoring. Recent syntheses seek to evaluate the relative impact of these types of interventions.<sup>3</sup> This paper has two objectives. The first objective is to propose widely comprehensible metrics for reporting the impact of interventions that seek to improve learning. Education economists and specialists generally report the effectiveness of an intervention in term of “standard deviations,” which may be difficult for non‐specialists to understand. For the vast majority of the population, from a Minister of Finance to a rural parent, what does it mean that a new educational policy increases student learning by 0.2 standard deviation? Not much. In this paper, we use two alternative approaches to quantify the impact sizes of different interventions. The first approach is to compare gains to learning in business‐as‐usual schooling, as above. We call these equivalent years of schooling (EYOS), as in, “A given learning intervention delivers the equivalent of 1.5 years of ‘business‐as‐usual’ schooling” in terms of learning outcomes. The second approach is to put a dollar amount on increased learning by estimating the long‐ term labor market returns, an approach often adopted in the cost‐effectiveness analysis of health

> 2 This is net enrollment, which is the percentage of children who are of primary‐school age that are enrolled in primary school. Gross enrollment – the number of children of any age that are enrolled in primary school divided by the number of children of primary‐school age – rose from 61 percent to 103 percent over the same period. Net enrollment numbers extend back to 1999, so previous years are a simple extrapolation relative to gross enrollment; however, that relationship was steady between 1999 and 2015.

> 3 There have been many syntheses of evidence to improve learning in recent years. Evans and Popova (2016) synthesize six of these synthesis studies. A recent synthesis which covers a wide range of recent interventions is Snilstveit et al. (2015), summarized in Snilstveit et al. (2016).

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