Disinterest in school, as a key psychological construct, is associated with reduced academic motivation, decreased school attendance, and weakened academic engagement, which may lead to consequences such as academic underperformance and school dropout. The aim of the present study was to develop and validate the Disinterest in School Scale among secondary school students in Ardakan during the 2024–2025 academic year. This research was applied in purpose and employed a correlational-psychometric design. The statistical population consisted of secondary school students in Ardakan, from which 324 participants were selected using cluster sampling. The research instruments included the researcher-developed Disinterest in School Scale, the School Burnout Inventory (Salmela-Aro & Näätänen, 2005), and the Academic Engagement Questionnaire (Fredricks et al., 2004). Data were analyzed using exploratory and confirmatory factor analyses, the Kaiser-Meyer-Olkin (KMO) sampling adequacy test, Bartlett’s test of sphericity, Cronbach’s alpha coefficient, and Pearson correlation coefficient, with SPSS version 26 and AMOS version 24. Results from exploratory factor analysis indicated that the scale comprises three factors: negative teacher interaction, structural disorganization, and academic meaninglessness, collectively explaining 68.22% of the total variance. Confirmatory factor analysis confirmed adequate model fit (RMSEA=.074; CFI=.954; GFI=.925). Convergent validity was established through a positive correlation with school-related burnout (r=.543), and divergent validity through a negative correlation with academic engagement (r=−.569). Additionally, the overall reliability of the scale, as measured by Cronbach’s alpha (α=.93), demonstrated excellent internal consistency. Overall, the findings indicate that the Disinterest in School Scale possesses robust psychometric properties and can be utilized for identifying at-risk students, designing targeted educational and psychological interventions, and preventing academic underachievement and school dropout.