In this article, Rachel Abenavoli, Natalia Rojas, Rebecca Unterman, Elise Cappella, Josh Wallack, and Pamela Morris argue that research-practice partnerships make it possible to rigorously study relevant policy questions in ways that would otherwise be infeasible. Randomized controlled trials of small-scale programs have shown us that early childhood interventions can yield sizable benefits. But when we move from relatively small, tightly controlled studies to scaled-up initiatives, the results are often disappointing. Here the authors describe how their partnership with New York City’s Department of Education, as the city rapidly rolled out its universal pre-K initiative, gave them opportunities to collect experimental and quasi-experimental evidence while placing a minimal burden on educators. They argue that this type of research can answer the most pressing ECE questions, which are less about whether ECE can make a difference and more about the conditions under which early interventions are effective at scale. They offer three recommendations for researchers, policy makers, and practitioners who are considering partnership work: build a foundation of trust and openness; carefully consider whether rigorous causal research or descriptive research is the right choice in a given situation; and be flexible, seeking opportunities for rigorous research designs that may already be embedded in early childhood education systems. (author abstract)