What’s the best way to persuade children to drink water instead of unhealthy, sugar-laced beverages? Do you:

A) Tell them it will make them more popular.

B) Tell them it will make them healthier.

C) Tell them it will make them smarter.

D) Just tell them to do it without explaining why.

The correct answer: B.

Turns out honesty is the most persuasive tactic, even for kids, while exaggerated claims and ungrounded mandates can potentially have a negative effect, according to new research by Szu-chi Huang, an associate professor of marketing at Stanford Graduate School of Business. The field study, performed in collaboration with UNICEF, was designed to determine the most effective way to steer schoolchildren in Panama away from unhealthy sodas and other sweetened drinks toward drinking water instead.

Story by Stanford Graduate School, Louise Lee. Cowritten with Daniella Kupor of Boston University, Michal Maimaran of Northwestern University, and Andrea Weihrauch of the University of Amsterdam, the paper will be published in the Journal of the Association for Consumer Research in January.