<p>School-related subjective well-being (SWB) has gained prominence in research on adolescent well-being. However, only a few instruments have been developed to specifically assess SWB in the school context. The aim of this study was to evaluate the psychometric properties of the Student Subjective Wellbeing Questionnaire (SSWQ) using data from Serbian primary school students (<i>N</i> = 435, mean age = 12.94, 55.2% female). An additional sample of secondary school students (<i>N</i> = 298, mean age = 16.42, 61.1% female) was recruited to test measurement invariance across educational stages. We found that the structure of the SSWQ was best represented by the exploratory structural equation model (ESEM) comprising four theoretically postulated factors: Joy of Learning, School Connectedness, Educational Purpose, and Academic Efficacy. The ESEM model demonstrated scalar invariance across gender and educational stages. Girls reported higher levels of Joy of Learning, School Connectedness, and Educational Purpose, whereas no significant gender differences were found in Academic Efficacy. Primary school students showed higher levels on all four dimensions of school-related SWB compared to secondary school students. Convergent validity of the ESEM factors was evidenced by meaningful associations with positive affect, life satisfaction, negative affect, and externalizing problems. The findings provide promising evidence for the utility of the SSWQ in measuring student SWB; however, further research is needed to establish its predictive and incremental validity.</p>