# the intervention.

We find that children whose parents participated in NEP experienced an increase of 0.43 standard deviation (SD) in a measure of cognitive development (receptive vocabulary), and an increase of 0.54 SD in a measure of personal-social development, relative to children in the control group. There were however no detectable medium-term impacts of NEP on executive function, or on internalizing and externalizing behaviors of children (point estimates are much closer to zero, sometimes negative, and never statistically significant). It is possible that positive shifts in these outcomes occurred shortly after the program ended and did not last, although we cannot verify this hypothesis.

The impact on language is mirrored by increases of similar or larger magnitude in indicators of the quality of the home environment, nurturing practices and a reduction in the report of harsh disciplinary strategies. Importantly, these changes are supported by significant improvements of similar magnitude in perceived parenting self-efficacy, in parental beliefs about their role in child development, as well as by perceived social support from friends and the community. All these results point to sustained changes in the parental self-efficacy, beliefs and in the parent-child interaction as key pathways for the sustained changes in cognitive and socio-emotional development.

These are remarkable results. They show how a parenting program which has low cost and is easy to implement at a national scale can produce long lasting changes in the lives of poor children and their families. It provides an interesting model for other countries, especially those struggling to provide valuable early childhood services due to severe lack of resources. One needs to consider, however, that Chile’s welfare system is well organized and staffed with a skilled and motivated workforce, which may have played a role in their success in implementing NEP.

Despite growing evidence on the effectiveness of parenting programs evaluated in small-scale trials, key questions remain relating to how to make these programs scalable, and how to sustain their impacts long-term. Individual home visits provide an opportunity to tailor activities to individual circumstances and personal barriers to behavioral change, but they are expensive to implement at scale.<sup>3</sup> Group parenting programs are less costly to implement at scale and favor the creating of support networks, but they offer less individualized attention and guided practice. The evidence of these programs, which is the type of program we examine here, is somewhat mixed.<sup>4</sup> Group-based interventions have been shown to shift parental knowledge about child development 3 A home visiting model in Jamaica that provides individualized support to parents to help them improve their child development found large effects on children’s developmental outcomes, sustained until adulthood (S. M. GranthamMcGregor et al. 1991, Gertler et al. 2014). Cross country replication of the Jamaican home visiting curriculum to other settings (such as Bangladesh, India and Colombia) has so far found impacts on child development in the short-term (O. P. Attanasio et al. 2014; Hamadani et al. 2006; Nahar et al. 2012; Vazir et al. 2013).

4 The systematic evidence in the LANCET series on Early Childhood Development suggests that interventions that directly engage the child in play experiences and guide caregivers in providing stimulating interactions, as well as give parents the opportunity to practice with their children and receive feedback, can be effective in remediating early disparities in child development (Black et al. 2017; Britto et al. 2016; Engle et al. 2007, 2011). A recent systematic meta-analysis, on the other hand, finds mean effect sizes in children’s language and cognitive outcomes of 0.32 SD for home-based studies, and 0.59 SD for group visit studies (Aboud and Yousafzai 2015).

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