Key takeaways and spoilers: 1. Scaling up is messy. Scale looks different in different contexts, and a "scalable" version of an intervention will need to fit into the existing systems and resource constraints. 2. The choice of the frontline providers - and the training and support provided to them - is critical. Volunteer providers need extensive training and continuous support, while seasoned professionals are overloaded with ongoing workload. And yet, reaching quality at scale is not possible without trained providers that are supported and supervised. 3. Reaching and retaining families is difficult at scale. Even when support and interest are there, demand is not automatic as families with young children are facing a multitude of challenges and pressures on their time. 4. Finally, achieving large-scale impact on outcomes is a journey. Even evidence-based interventions require time and iteration to show effectiveness at scale. Iteration, adaptation (as opposed to more of the same), attention to quality are all key. Background/Objectives: As an independent research group, we examined parent and child outcomes of three different parenting programs delivered at scale. The programs were implemented in Bhutan, Serbia and Zambia by different organizations. Methods: Mixed methods included a caregiver interview using the HOME Inventory, a direct child assessment using the Global Scales of Early Development (GSED) and focus group discussions with caregivers (FGD). Sampled mothers and children were randomly selected for the HOME/GSED: Bhutan n = 432, Serbia n = 636, Zambia n = 1024. Over 40 mothers and fathers of children under 3 years were purposively selected for FGD. Intention-to-treat and secondary regression analyses of attendees and non-attendees were conducted on the HOME and GSED; FGDs were subject to content analysis. Results: Parenting practices were found to be minimally (Bhutan) or modestly (Zambia) higher for caregivers who attended group sessions. Caregivers in Serbia who recalled receiving play messages had higher HOME scores. Child outcomes showed small (Bhutan) or no differences (Serbia, Zambia) associated with participation. Conclusions: Explanations focused on limits to program participation in scaled programs, the need for pilot evaluations to ensure that the program design is effective, and the need to monitor delivery quality and other implementation processes.