This study examines how students' support, self-esteem, and schoolwork difficulties are related to the development of students' subjective well-being (SWB), which consists of social relations and self-fulfillment. The participants (n = 326, aged 16 years) were followed for the first 2 years of general upper secondary education in Finnish schools. The first-year results in the path model showed that students who received more support or had better self-esteem were more likely to have better SWB, but students with schoolwork difficulties had lower SWB. The results also indicated that SWB in the second year was strongly predicted by SWB in the first year. All autoregressive effects of the variables from the first to second year were significant, but schoolwork difficulties had the highest stability, and support had the lowest stability. Moreover, the mediation effects between the variables from the first to second year suggested that students who had low SWB in the first year experienced more schoolwork difficulties in the second year. In practice, it was an important finding that, in both years, the school staff members could positively impact students' SWB through support, even though the received support was insufficient to reduce the negative effect of schoolwork difficulties on SWB.