We examined the additive associations of two motivational beliefs (growth mindset and academic self-efficacy) and self-regulation with mathematics and English Language Arts (ELA) scores, as well as the interplay of students' beliefs and self-regulation skills, controlling for previous test scores. We tested whether these pathways differed across three mutually exclusive levels of economic risk: (1) low-risk students; (2) students receiving free and reduced price meals (FRPM); and (3) students identified as homeless and highly-mobile (HHM). Our results showed that motivational beliefs and self-regulation skills interact to promote academic achievement. Greater levels of growth mindset were related to higher academic achievement only for HHM students with higher levels of self-regulation. [This paper was published in "Journal of Applied Developmental Psychology" v82 Article 101442 2022.]