Development and psychometric evaluation of the School Adjustment Scale for Turkish middle school students

This study aimed to develop and conduct a comprehensive psychometric evaluation of a scale designed to measure middle school students' school adjustment levels (School Adjustment Scale for Middle School Students - SASMSS). The item pool created as a result of a literature review conducted by researchers was subjected to expert evaluation for content validity, involving a panel of specialists in educational sciences and psychology. The research was carried out using a methodological research design. Data were collected from three independent convenience samples: Sample 1 (n = 1242) for exploratory factor analysis (EFA), Sample 2 (n = 1222) for confirmatory factor analysis (CFA), and Sample 3 (n = 1326) for CFA replication and measurement invariance analysis. The EFA results revealed a three-factor structure, comprising academic, social, and behavioral adjustment domains, with six sub-dimensions (academic interest, academic competence, externalization behavior, adherence to rules, prosocial behaviors, and friendship relations), explaining 42.93% of the total variance. The hypothesized structure was supported by CFA with excellent fit indices (CFI = .93, TLI = .92, RMSEA = .04, SRMR = .04). Measurement invariance analysis across gender further demonstrated that the scale exhibits equivalent psychometric properties for male and female respondents. Additionally, Differential Item Functioning (DIF) analysis based on ordinal logistic regression revealed no significant gender-related item bias, reinforcing item-level fairness. These findings provide strong evidence for the validity, reliability, and fairness of the SASMSS scale within the Turkish educational context.