In a mixed‐methods study following 1551 adolescents from eight diverse schools across the US, a large majority demonstrated (a) strong norms of actively open‐minded thinking (AOT) and (b) a widespread capacity for AOT. Students from two public (government) schools, two private (public) schools, and two charter (academy) schools were followed for 18 months over the transition from middle school to high school, with data collected in each semester of the eighth grade and ninth grade year. The study included an unusually varied set of approaches to assess AOT values and habits, including a rating scale, two new multiple choice measures, teacher reports from three teachers per student, peer nomination, and interviews with subsets of the larger sample. These varied measures converged to reveal widespread openness to disagreement, desire for understanding, and pluralistic norms. In interviews, participants demonstrated AOT in three powerful ways: deep web search for ideas, epistemic empathy, and pluralistic thinking . Moreover, repeated administration of measures indicated moderate intertemporal reliability of this trait, with six‐month test‐retest correlations ranging from .27 to .59 depending on the measure. This research suggests that existing capacities for AOT could be more fruitfully leveraged and supported by educators, helping students to capitalise on their own values and intuitions as they develop into mature critical thinkers.