Here we evaluate the potential for growth mindset interventions (that teach students that intellectual abilities can be developed) to inspire adolescents to be “learners” — that is, to seek out challenging learning experiences. In a previous analysis, the U.S. National Study of Learning Mindsets (NSLM) showed that a growth mindset could improve the grades of lower-achieving adolescents, and, in an exploratory analysis, increase enrollment in advanced math courses across achievement levels. Yet, the importance of being a “learner” in today’s global economy requires clarification and replication of potential challenge-seeking effects, as well as an investigation of the school affordances that make intervention effects on challenge-seeking possible. To this end, the present article presents new analyses of the U.S. NSLM (N = 14,472) to (a) validate a standardized, behavioral measure of challenge-seeking (the “make-a-math worksheet” task), and (b) show that the growth mindset treatment increased challenge-seeking on this task. Second, a new experiment conducted with nearly all schools in 2 counties in Norway, the U-say experiment (N = 6,541), replicated the effects of the growth mindset intervention on the behavioral challenge-seeking task and on increased advanced math course-enrollment rates. Treated students took (and subsequently passed) advanced math at a higher rate. Critically, the U-say experiment provided the first direct evidence that a structural factor—school policies governing when and how students opt in to advanced math — can afford students the possibility of profiting from a growth mindset intervention or not. These results highlight the importance of motivational research that goes beyond grades or performance alone and focuses on challenge-seeking. The findings also call attention to the affordances of school contexts that interact with student motivation to promote better achievement and economic trajectories.