In this paper, we study the effectiveness of social labeling as a technique to promote pro-environmental behaviors in children, and examine more specifically the potential moderating effect of children’s age. We run an experiment on a sample of 115 3rd to 6th grade children and show that 1/ children exposed to a social labeling actually declare more pro-environmental behaviors and that 2/ children at an intermediate age (between 9 years and a half and 11 years and a half) are the most responsive to the technique, underlying an inverted-U relationship between social labeling effectiveness and children's age. These results contribute to a better theoretical understanding of social labeling mechanisms and suggest implications for public policy makers.