Programs implemented by nongovernmental organizations (NGOs) are often more effective than comparable efforts by other actors, yet relatively little is known about how implementer identity drives final outcomes. By combining a stratified field experiment in India with a triple-difference estimation strategy, we show that a local development NGO’s prior engagement with target communities increases the effectiveness of a technology promotion program implemented in these areas by at least 30%. This “NGO reputation effect” has implications for the generalizability and scalability of evidence from experimental research conducted with local implementation partners.