Formative assessment has been long emphasised as a powerful means for enhancing science learning. However, there is still a lack of research to investigate the impacts of formative assessment on both students' motivational beliefs and behaviours in science learning. This study examined such impacts using data from six Western and six East Asian countries/economies in PISA 2015. 96,491 15-year-old students were included. The SEM analysis of overall data showed that (i) formative assessment had both direct effects on students' science learning behaviours and indirect impacts mediated by students' motivational beliefs and (ii) the total effect of teacher feedback on science learning behaviours was greater than adaptive instruction. The comparison between Western and East Asian datasets indicated that (i) the impact of teacher feedback on East Asian students' motivational beliefs was greater than that on their Western counterparts; (ii) the impact of adaptive instruction on Western students' motivational beliefs was greater than that on East Asian counterparts; and (iii) the direct impacts of teacher feedback and adaptive instruction on science learning behaviours were similar for both groups of students. Suggestions were made on how to effectively implement formative assessment to enhance science learning in different cultural contexts.