Mathematics teachers’ beliefs are central to mathematics teaching and student learning. Because different aspects of motivation and affect—particularly enjoyment—primarily develop within the classroom context, examining how different teachers’ beliefs may affect student outcomes in mathematics is imperative. The current study examines teachers’ beliefs about the nature and learning of mathematics in connection to students’ motivation (i.e. intrinsic value, utility value and perceived competence) and enjoyment of mathematics across different settings by considering students’ mathematics achievement, gender and classroom composition (i.e. socioeconomic and behavioural). Data were collected from 3rd- and 4th-grade mathematics teachers (N = 686) and their students (N = 11,782) in six countries (i.e. Norway, Finland, Sweden, Portugal, Estonia and Serbia). A two-level structural equation modelling technique (TSEM) (i.e. student level and classroom level) with random slopes was employed to address our research questions. The results indicate that students’ intrinsic value and perceived competence positively relate to their enjoyment of mathematics in all six countries. Teachers’ beliefs about the nature and learning of mathematics moderate the within-classroom relationship between boys and girls and the motivation and enjoyment of learning mathematics in Portugal and Norway. Unlike boys, girls consistently perceive themselves as less competent in mastering mathematics, even in primary school. Classroom socioeconomic composition had a more pronounced influence on teachers’ beliefs in Sweden, Norway and Serbia. In relation to teachers’ beliefs, classroom behavioural composition was relevant in Estonia and Sweden. In Finland and Norway, classroom composition was essential to boys’ and girls’ differential motivation and enjoyment of mathematics learning.