We conduct a randomized experiment to evaluate the effect of a light-touch low-cost psychological intervention on psychological well-being and economic decision-making in a developingcountry setting. Residents of an informal settlement in Kenya were randomly assigned to participate in best-practice exercises designed to promote gratitude, self-affirmation, and aspirations. We show that although we were successful in manipulating the psychological construct (reported gratitude increased 0.3SD), there is no evidence that the intervention affected overall psychological well-being, beliefs, or aspirations. We also see no effects on real-incentive tasks measuring cognitive control or temporal discounting. Our results are important because lighttouch positive psychology interventions are being widely promoted in workplaces and schools worldwide as a low-cost solution to dramatically improve psychological well-being. We thank James Reisinger, Matthew Cohen and Lucy Rimmington for excellent research assistance, and James Vancel and the staff of the Busara Center for Behavioral Economics for implementation. We are grateful for comments to Leslie Martin, Sendhil Mullainathan, Tom Wilkening, and Jenny Williams. This research was supported by the Faculty of Business and Economics at the University of Melbourne and NIH R01AG039297 (Common Fund).