Poor psychosocial working conditions in school have consistently been shown to be associated with adverse health among adolescents. However, the relationships between school demands, teacher support, and classmate support and positive aspects of health have not been explored to the same extent. The aim of this study was to examine differences in psychosocial working conditions in school and in life satisfaction by gender and by grade, and to investigate the association between psychosocial working conditions in school and life satisfaction among boys and girls, and among students in different grades. Data from the Swedish Health Behavior in School-Aged Children (HBSC) study of 2017/18 were used, consisting of 3614 students in Grades 5, 7, and 9 (~11, 13, and 15 years). Psychosocial working conditions in school were captured by indices of perceived school demands, teacher support, and classmate support. Life satisfaction was measured by the 11-step Cantril’s ladder (using cutoffs at >5 and >8, respectively). Whereas girls reported higher school demands than boys, higher levels of teacher and classmate support were reported by boys. Students in lower grades reported lower school demands but higher levels of teacher and classmate support compared with students in higher grades. Boys and students in lower grades were more likely to report high life satisfaction compared with girls and students in higher grades. Results from binary logistic regression analyzes showed that school demands were inversely associated with life satisfaction, and that higher levels of teacher support and classmate support were associated with high life satisfaction. These results were found for both boys and girls, and for students in all grades. The findings indicate that schools have the potential to promote positive health among students.