Reporting private information is a key part of economic decision making. A recent litera-ture has found that many people have a preference for honest reporting, contrary to usualeconomic assumptions. In this paper, we investigate whether preferences for honesty aremalleable and what determines them. We experimentally measure preferences for honestyin a sample of children. As our main result, we provide causal evidence on the effect of thesocial environment by randomly enrolling children in a year-long mentoring programme.We find that, about four years after the end of the programme, mentored children aresignificantly more honest.