We study the effectiveness of “social labeling” to promote pro-environmentalbehaviors in preadolescents, and examine the moderating effect of age. We run an experiment on 115 preadolescents and show that (1) tweens exposed to a social labeling declare more pro-environmental behaviors, (2) those behavioral concerns are sustained over an extended period of time, and (3) preadolescents between 9.5 and 11.5 year-old are the most responsive to the technique, underlying an inverted-U relationship between social labeling effectiveness and age. Referring to previous research on children, persuasion knowledge and social labeling, we propose theoretical explanations and (responsible) managerial implications.