Does motivation towards science mediate the relationship between parental support and adolescent science achievement? A comparison of two countries

• Stronger effect of parental support on motivation in Korea than in the U.S. • Significant association between parental support and achievement only in Korea. • Mediating role of science motivation between parental support and achievement. • Cross-cultural differences in mechanisms linking support, motivation, and achievement. • Importance of science motivation in explaining parental support’s effect on outcomes. This study explored the mediating role of motivation towards science and the moderating role of cultures in the relationship between parental support and adolescent science achievement. We conducted a moderated mediation analysis of the 2015 Programme of International Student Assessment data from Korea ( n = 5581) and the United States ( n = 5712). The results imply that culture moderated the effects of parental support on students’ science motivation and achievement: the predictive effect of parental support on intrinsic motivation was stronger in Korea than in the United States, and parental support significantly predicted higher science achievement in Korea but not in the United States. Furthermore, adolescents’ motivation towards science mediated the relationship between parental support and science achievement. The study sheds light on different mechanisms underlying parental support, adolescents’ motivation towards science, and science achievement. The findings also highlight the need to consider adolescents’ motivation towards science when explaining the effect of parental support on their science performance. Finally, the findings advance motivational theories, particularly in the science education field.