Presentation delivered at CIES 2017 (Atlanta). The Tayari intervention’s randomized controlled trial design is structured to allow for causal inference of Tayari’s impact on school readiness. Previous research has shown how similar ECD programs have affected learning outcomes, but the literature remains silent on how individual children’s skills transition over time. The Tayari longitudinal research design allows us to estimate growth trajectories of individual children. This is particularly salient as the literature lacks models for how literacy and numeracy skills interact with the executive functioning and socioemotional skills that Tayari investigates interact with each other over time. The Tayari longitudinal study follows more than 3100 learners across three rounds of data collection and a wider range of sills than is available in the Tayari impact evaluation. Given how little is known about how children’s core ECD skills grow, the Tayari longitudinal intervention estimates first how the skills grow in the normal control condition, and then how the Tayari program affects growth rates and relationships between learning elements. Finally, the Tayari longitudinal study will continue to develop an understanding of how children transition skills between the two levels of pre-primary in Kenya to the primary education sector where the Tusome literacy program is being implemented at national scale.