This study reports on the initial development and validation of the Student Subjective Wellbeing Questionnaire (SSWQ) with a sample of 1,002 students in Grades 6-8. The SSWQ is a 16-item self-report instrument for assessing youths' subjective wellbeing at school, which is operationalized via 4 subscales measuring school connectedness, academic efficacy, joy of learning, and educational purpose. The conceptualization and development of the SSWQ's subscales and items are described, and results from a series of preliminary psychometric analyses are reported. Findings indicated that the SSWQ was characterized by 4 conceptually sound latent factors, that these 4 first-order factors were robust indicators of a single second-order factor (i.e., student subjective wellbeing), that all subscales and the composite scale demonstrated at least adequate construct reliability and internal consistency, and that the estimated latent-means for all first-order and second-order factors were invariant across gender. Moreover, results from bivariate correlations and a latent-variable path analysis provided evidence in support of the construct validity of the SSWQ's scales and latent factors, showing strong associations with other student wellbeing indicators (i.e., school prosociality and academic perseverance), while findings from binary logistic regressions demonstrated that overall student subjective wellbeing levels, based on composite scores from the SSWQ, were mildly to-strongly associated with a variety of self-endorsed risk factors (e.g., aggression and self-harm) and protective factors (e.g., social support and physical exercise). Implications for theory, research, and the practice of school psychology are discussed.