<p>Adaptive functioning in school settings remains understudied in ADHD research, despite its critical role in supporting students in navigating social, organizational, and emotional demands in daily school life. Existing tools often prioritize symptom severity or isolated domains (e.g., executive function, academics, and behaviors), lacking a multidimensional, school-contextualized assessment. This study introduces the Adaptive Functioning in School Questionnaire (AFSQ), a teacher-reported measure designed to identify adaptive functioning challenges students face in school by assessing the following five domains: 1) social and behavioral adaptation; 2) practical organization; 3) academic task management; 4) emotional comprehension and expression; and 5) emotion regulation and conflict resolution. Participants included 564 students with ADHD (<i>M</i> age = 9.42 years) and 93 community peers (90% non-ADHD; <i>M</i> age = 9.36 years), along with their teachers. Factor analyses confirmed the AFSQ’s robust five-factor structure, and convergent validity was supported by strong correlations with executive function (|<i>r|</i> =.62–.71) and social skills (|<i>r|</i> =.58–.66). Students with ADHD exhibited greater adaptive challenges across all domains compared to neurotypical peers, with large effect sizes (<i>d</i> =.82–1.34). While inattention predicted adaptive functioning broadly, Oppositional Defiant Disorder/symptoms (ODD) uniquely exacerbated social-behavioral and emotional challenges in students with ADHD, highlighting the need for tailored interventions in comorbid cases. The AFSQ demonstrates strong reliability (<i>α</i> =.83–.96) and validity, offering educators and clinicians a school-specific tool to identify individualized support needs and guide targeted support strategies beyond symptom profiles.</p>