The proliferation of information and divergent viewpoints in the 21st century requires an educated citizenry with the ability to critically evaluate information and make informed decisions. To meet this demand, adaptive epistemic understandings and beliefs about the nature of knowledge are needed, such as believing that scientific knowledge is evolving (development of knowledge) and needs to be justified through experimentation (justification of knowledge). Our study is the first to use nationally representative samples from 72 countries/regions (PISA 2015 database; N = 514,119 students) to examine how scientific epistemic beliefs about development and justification of knowledge in science are associated with students' science motivation, achievement, and career aspirations in the STEM fields, as well as the cross-national generalizability of these relations. Results showed that (a) students who had more adaptive beliefs about knowledge being changeable and stemming from experimentation were likely to have high science self-efficacy, utility value, and particularly high intrinsic value; (b) epistemic beliefs were more strongly linked to science achievement than were motivational constructs; (c) the positive relation between epistemic beliefs and STEM-related career aspirations was largely explained by motivation and achievement; (d) the pattern of results generalized well across societies. Our findings suggest that epistemic beliefs are substantially positively associated with adolescents' science learning, implying that developing effective interventions that focus on development and justification of knowledge would be fruitful for promoting science educational outcomes. Educational Impact and Implications StatementHolding adaptive epistemic beliefs about the nature of scientific knowledge is critical in distinguishing accurate and useful information from diverse, less trustworthy sources in the digital era. Based on data from more than half a million 15-year-old students from 72 countries/regions, we found that adolescents with more adaptive epistemic beliefs tend to have higher science achievement, feel more self-efficacious, be more intrinsically and extrinsically motivated to engage in science learning, and have higher aspirations to pursue a STEM-related career. Notably, epistemic beliefs are more strongly linked to science achievement than are motivational constructs. Consistent patterns across societies suggest that preparing students for 21st century challenges will require policy initiatives that ensure epistemic cognition is a core component of science education and scientific literacy.

Individuals’ subjective well-being (SWB) is an important marker of development and social progress. As psychological health issues often begin during adolescence, understanding the factors that enhance SWB among adolescents is critical to devising preventive interventions. However, little is known about how institutional contexts contribute to adolescent SWB. Using Programme for International Student Assessment (PISA) 2015 and 2018 data from 78 countries ( N = 941,475), we find that gender gaps in adolescents’ SWB (life satisfaction, positive and negative affect) are larger in more gender-equal countries. Results paradoxically indicated that gender equality enhances boys’ but not girls’ SWB, suggesting that greater gender equality may facilitate social comparisons across genders. This may lead to an increased awareness of discrimination against females and consequently lower girls’ SWB, diluting the overall benefits of gender equality. These findings underscore the need for researchers and policy-makers to better understand macro-level factors, beyond objective gender equality, that support girls’ SWB.