This chapter compares three versions of the same home visiting model, which was gradually scaled-up from an efficacy trial (“proof of concept”) in Jamaica, to a pilot in Colombia, to an at-scale program in Peru. It describes the design, implementation and impacts of these three programs. It analyzes the threats to scalability in each of these experiences and discusses how they could have affected program outcomes, with a focus on three of the elements of the economic model of scaling in Chapter 6 (Al-Ubaydli et al.): appropriate statistical inference, properties of the population, and properties of the situation. The chapter reflects on lessons learned to mitigate the threats to scalability and on how research and evaluation can be better aligned to facilitate and support the scaling-up process of early child development interventions.