data collection with a classroom observation survey conducted in all the preschools within the sample villages.

The household survey included information about family structure, household wealth, and other socioeconomic background characteristics.The caregiver survey included questions regarding the child’s preschool enrollment and socio-emotional development, as well as 25 questions about parenting practices. The latter measure three key dimensions of parenting: “cognitive parenting”, “emotional parenting”, “and negative parenting”. More cognitive parenting means parents are more likely to engage in activities that contribute to the development of their child’s cognitive competencies (e.g. by playing games, reading books, or playing with toys). More socioemotional parenting means parents interact more in ways that provide emotional support and responsiveness (e.g. comforting, encouraging or complimenting the child). More negative parenting means parents are more likely to use harsh or punitive approaches to discipline their child. Last, the survey included information about home visits, D2D activities, and participation in the HBP, as well as the caregiver’s perceived returns to education, and a short test of the respondent’s nonverbal reasoning ability (based on the Raven’s Progressive Matrices Test).

The approximately 45-minute child assessment included a comprehensive battery of cognitive tests (executive function, language, early numeracy, fine motor development and, at baseline and midline only, gross motor development) as well as anthropometric measures (height and weight). Most of the child tests were based on the Measuring Early Learning Quality and Outcomes (MELQO) toolkit. (See UNESCO (2017) for a description of the measures-of-development process and Raikes et al. (2019) for evidence of validity).<sup>22</sup> Additional child tests were added to the MELQO items to increase the sensitivity and breadth of the child assessment. The additional tests included the following: the Dimensional Change Card Sort (Zelazo, 2006)<sup>23</sup> ; a receptive vocabulary test based on picture recognition; a test for knowledge of reading concepts (based on a monitoring tool used by the Cambodian Ministry of Education); and a sustained attention test. Children’s socio-emotional development was measured using the caregiver-reported Strengths and Difficulties Questionnaire (SDQ). Using these tests, we create two indexes: a cognitive development index which aggregates executive function, language, early numeracy, and fine motor scores and a socio-emotional index which aggregates the individual dimensions of the SDQ.<sup>24</sup>

> 22An in-depth discussion of midline child tests, scoring methods, cultural adaptations, pretesting procedures, and questions about parenting practices can be found in Berkes et al. (2019).

> 23No cultural adaptation of words or pictures was conducted since the test was working well in field pilots and changes were not deemed necessary by the local staff.

> 24Individual tests were scored and standardized to ensure that their variance equally contribute to the composite score. For almost all tests, we assign one point per correct answer and zero when the child was unable to complete the practice trial of a test. We calculated each test score by summing all correct answers and standardizing them using the control group sample mean and the control group sample standard deviation. All standardized test scores of one domain (e.g.,

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