This chapter examines the skills and abilities of young children in the most disadvantaged communities in low income countries through the lens of IDELA data. It emphasizes the need to move away from national averages in order to understand the ECD landscape for children at the bottom of the pyramid and for researchers to use a multi dimensional tool, like IDELA, in order to gain a rich view of early childhood development that incorporates not only math literacy and numeracy skills, but also social emotional learning, motor development, and executive function skills. It concludes that work towards SDG 4 provides an unprecedented opportunity for gains in early childhood development and proven, rigorous tools like IDELA will help governments and policy makers achieve these improvements.