Three subscales of the Stanford Binet Intelligence Scales (visual-spatial processing, working memory, and fluid reasoning) were combined to estimate children’s non-verbal cognitive ability. The Leiter test was used to evaluate the capacity to maintain attention, which has been identified as a critical metric of school readiness and is an important component of executive function (Duncan et al. 2007). The Woodcock Muñoz (WM) memory of phrases test requires children to repeat words and sentences with an increasing order of difficulty; it is also considered a measure of working memory, which is a component of executive function. The Peabody Picture Vocabulary Test (PPVT-III) is a test of receptive vocabulary knowledge and was administered to the children and their primary caregivers.

Z-scores were calculated for each of the above tests from two-month, age-specific means and standard deviations in each age category.

# _Learning Tests and Child Enrollment_

In addition to the measures of cognitive and language development, two tests of learning outcomes were incorporated when children were school age in 2011: one for mathematics and the other for early literacy skills. The tests were adaptations of the Early Grade Reading Assessment (EGRA) (Gove and Wettenberg 2011) and the Early Grade Mathematics Assessment (EGMA) (Rubens 2009) instruments developed by USAID and widely used in other French-speaking African countries. The literacy test ranged from basic assessment of auditory comprehension, recognition of letters and key basic words, to more complex ability of reading and comprehension of a text. The mathematics test includes basic number identification, comparison of numbers, basic arithmetic (addition, subtraction, multiplication, and division) and word problems involving addition and subtraction. After translation, the Malagasy versions of these tests were systematically and rigorously pretested and were found to be informative even among children who had not attended school. For example, many children knew how to count and answer the simplest word problems even if they had not attended formal schooling. Short stories that were part of the original test were rewritten during the pretesting phase so that questions associated with auditory comprehension would be accessible to children who were illiterate.

# _SES and Sociodemographic Characteristics_

The key proxy of SES used in the analyses is a household wealth index in 2004 when children were 0–3 years, divided into quintiles. The index was constructed using principal component analysis of key durables, assets and dwelling conditions<sup>2</sup> (Filmer and Pritchett 2001). This SES proxy is less likely to suffer from the concern about measurement error that generally affects income variables. Furthermore, an index for wealth is often used in the analysis of SES gradients in child outcomes in both developed and developing country contexts, and commonly adopted in descriptive analysis of Demographic and Health Surveys. As described in greater detail below, a full set of dummy variables for wealth quintiles were included in our regressions, and the results translated back into English to ensure linguistic and functional equivalence. More information on each child test is available in appendix 1.

> 2. The wealth index is the first principal component of the following variables: walls, floors, roof, home ownership, whether the toilette is shared, whether household has access to safe water, ownership of chairs, phone, motor vehicle, cattle ownership, and poultry ownership. The sample is representative of rural and small urban villages (excluding large cities in all regions and the capital).