Research on parental involvement is broad and specifies diverse kinds of parental practices that have specific associations with children's learning outcomes. However, the involvement of parents in education, the dynamics of parent-child interactions and the actions and practices they employ and their impact on student's motivation and achievement are intricate processes characterised by numerous intervening variables that require further clarification. In this study, we aimed to examine the association between parental beliefs and involvement and their children's motivation and mathematics achievement. Data were collected from 8071 third- and fourth-graders from six European countries and their parents. Students fulfilled the Expectancy-Value Scale, self-reporting on motivational aspects towards mathematics and performed two math tests to assess their performance. Parents also reported on their math attitudes, mindsets and involvement practices with their children. Data analysis was performed using structural equation modelling. Several theoretically meaningful associations were found in the tested model, showing the detrimental impacts of a fixed mindset on parents' practices. Furthermore, we found significant relationships between parents' attitudes towards mathematics, their practices and students' perceptions of math-related values and cost. Finally, associations between parental practices, the child's outcomes and the association between children's mathematics motivation and achievement were also observed. Some implications are presented, particularly concerning interventions with parents.