A global priority for the behavioural sciences is to develop cost-effective, scalable interventions that could improve the academic outcomes of adolescents at a population level, but no such interventions have so far been evaluated in a population-generalizable sample. Here we show that a short (less than one hour), online growth mindset intervention—which teaches that intellectual abilities can be developed—improved grades among lower-achieving students and increased overall enrolment to advanced mathematics courses in a nationally representative sample of students in secondary education in the United States. Notably, the study identified school contexts that sustained the effects of the growth mindset intervention: the intervention changed grades when peer norms aligned with the messages of the intervention. Confidence in the conclusions of this study comes from independent data collection and processing, pre-registration of analyses, and corroboration of results by a blinded Bayesian analysis.

There are many promising psychological interventions on the horizon, but there is no clear methodology for preparing them to be scaled up. Drawing on design thinking, the present research formalizes a methodology for redesigning and tailoring initial interventions. We test the methodology using the case of fixed versus growth mindsets during the transition to high school. Qualitative inquiry and rapid, iterative, randomized “A/B” experiments were conducted with ~3,000 participants to inform intervention revisions for this population. Next, two experimental evaluations showed that the revised growth mindset intervention was an improvement over previous versions in terms of short-term proxy outcomes (Study 1, N=7,501), and it improved 9th grade core-course GPA and reduced D/F GPAs for lower achieving students when delivered via the Internet under routine conditions with ~95% of students at 10 schools (Study 2, N=3,676). Although the intervention could still be improved even further, the current research provides a model for how to improve and scale interventions that begin to address pressing educational problems. It also provides insight into how to teach a growth mindset more effectively.

What can be done to reduce unhealthy eating among adolescents? It was hypothesized that aligning healthy eating with important and widely shared adolescent values would produce the needed motivation. A double-blind, randomized, placebo-controlled experiment with eighth graders (total n = 536) evaluated the impact of a treatment that framed healthy eating as consistent with the adolescent values of autonomy from adult control and the pursuit of social justice. Healthy eating was suggested as a way to take a stand against manipulative and unfair practices of the food industry, such as engineering junk food to make it addictive and marketing it to young children. Compared with traditional health education materials or to a non–food-related control, this treatment led eighth graders to see healthy eating as more autonomy-assertive and social justice-oriented behavior and to forgo sugary snacks and drinks in favor of healthier options a day later in an unrelated context. Public health interventions for adolescents may be more effective when they harness the motivational power of that group’s existing strongly held values.

Adolescents are exposed to extensive marketing for junk food, which drives overconsumption by creating positive emotional associations with junk food1–6. Here we counter this influence with an intervention that frames manipulative food marketing as incompatible with important adolescent values, including autonomy from adult control and social justice. In a pre-registered, longitudinal, randomized, controlled field experiment, we show that this framing intervention reduces boys’ and girls’ implicit positive associations with junk food marketing and substantially improves boys’ daily dietary choices in the school cafeteria. Both of these effects were sustained for at least 3 months. These findings suggest that reframing unhealthy dietary choices as incompatible with important values could be low-cost, scalable solution to producing lasting, internalized change in adolescents’ dietary attitudes and choices.

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