Programs implemented by non-governmental 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 tripledifferences 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 percent. This “NGO reputation effect” has implications for the generalizability and scalability of evidence from experimental research conducted with local implementation partners.