The impact of ADHD symptoms, class size, and classroom area on university students’ selective attention

The purpose of this study is to investigate how three factors—stable traits (the severity of ADHD symptoms), momentary states (mental fatigue), and classroom context (class size and area)—influence students’ attention in actual classroom settings. The study compares the distinct and combined contributions of trait, state, and context using the time-pressured d2 Test of Attention, which is given in situ and guided by the dual-pathway and cognitive-energetic models of ADHD. A cross-sectional survey design was employed to examine the relationships among ADHD symptom severity, mental fatigue, and student attention. Data were collected in April 2025 from 134 Iranian university students during regular classroom sessions. ADHD symptom severity was measured using the Adult ADHD Self-Report Scale (ASRS-v1.1) 6-Item Screener, mental fatigue with the Mental Fatigue Scale (MFS), and attention through the D2 Test of Attention, which assessed accuracy and processing speed under time constraints. Classroom size (square meters) and class size were included as control variables. Data analysis was performed using Partial Least Squares Structural Equation Modeling (PLS-SEM) with SmartPLS 4 to evaluate both direct and moderating effects. The findings revealed a significant negative relationship between ADHD symptom severity and student attention, indicating that higher ADHD symptoms were associated with lower attention performance. However, the hypothesized moderating effect of mental fatigue on this relationship was not supported. Additionally, classroom size and the class size showed significant effects, with smaller class sizes and more spacious classrooms linked to increased attention. This study underscores the significant impact of ADHD symptom severity on student attention, independent of mental fatigue. It highlights the importance of classroom factors in shaping attentional performance and calls for future research to further explore these dynamics through longitudinal and experimental designs. We integrate classroom ecology—class size and usable area per student—into an in-situ objective attention task (d2), isolating trait (ADHD symptoms) from state (mental fatigue) influences. Despite theory-driven expectations, mental fatigue did not moderate ADHD’s impact, indicating a state-insensitive, trait-dominant pathway under time-pressured selective-attention demands. These findings refine dual-process and cognitive-energetic accounts by highlighting environmental context (space and group size) as the more consequential amplifier of ADHD-linked attentional deficits.