In an effort to improve learning for young children and respond to preschool fade out, some districts are working on "PreK-3" initiatives to create better connected learning pathways for children. In these pathways, primary grades continue to build on what children learn in preschool; they also present potential implementation challenges that are not accounted for in the literature. Using conceptual tools from institutional theory and empirical evidence from a study of two school districts, we show how challenges arise as districts try to bridge the divergent and entrenched institutional systems of preschool and elementary. Our findings suggest that these systems are each held in place by their own set of regulative, normative, and cultural-cognitive mechanisms that reinforce one another thereby providing an explanation for why beliefs and practices are so resistant to change. This analysis also points to practical implications that may lead to better connections and learning experiences for young children.