Current society creates stress and pressure to achieve for many children and youth. Students’ motivation and well-being are topical issues, and increasingly younger students experience low motivation and study-related strains that hinder learning and well-being. Consequently, there is a need to study the role of motivational and emotional risk factors for young students’ learning and well-being. The overall objective of this project is to examine the developmental and situational dynamics between students’ math motivation, school well-being, performance, and educational aspirations across primary and lower secondary education. The project takes into account developmental, situational, and contextual perspectives as well as their interaction. The aim is threefold. Aim 1 addresses the long-term developmental dynamics between students’ motivation, school well-being, and educational outcomes across the primary and lower secondary school years (Grades 4–8). Aim 2 addresses the situated nature of students’ motivational beliefs and school well-being: the stability of situated math motivation and school well-being within math lessons, and across days and weeks. Aim 3: addresses how contextual characteristics (school transitions, situated context) relate to students’ motivational beliefs and school well-being. The aims are approached using both longitudinal and situational data. The longitudinal data (N ≈ 830) lays the foundation for the project with the investigation of motivation, well-being, performance, and educational aspirations across Grades 4–8. This data will be extended with in-the-moment measures of students’ (N ≈ 550) situational motivation and well-being within and across math lessons. As the focus is to study individual differences and development, models estimated within the mixture model framework will mainly be conducted (including latent profile and transition analysis, and growth mixture modeling). Both antecedents (e.g. gender, SES) and predictions (e.g. performance, aspirations) of the latent profiles will be considered. All objectives have broad international relevance both scientifically and in terms of educational practice. The project increases our understanding of how and why math motivation and well-being develop across the critical transition from primary to lower secondary school and is among the first to incorporate a situational perspective of in the moment math motivation and well-being across school days and weeks.