Traditional variable-centered research on executive functions (EFs) often infers intraindividual development using group-based averages . Such a method masks meaningful individuality and involves the fallacy of equating group-level data with person-specific changes . We used an intensive longitudinal design to study idiographic executive function fluctuation among ten boys from Grade 4 . Each of the participants completed between 33 and 43 measurement occasions (M = 38.8) across approximately three months . Data were collected remotely using a computerized short version of the Dimensional Change Card Sort task . Multi-group analyses of three participant pairs (Participants 5 and 3 , 5 and 2, and 5 and 6) demonstrated that Participant 5 differed from Participants 3 and 2 in different ways but Participants 5 and 6 were similar in all comparisons . Dynamic structural equation modeling demonstrated unique individual trajectories, which were not represented by the trajectory of group-averages . Although more than half of the participants showed a negative association between EFs and inattention, two participants showed a positive association between EF and inattention . This study demonstrated meaningful person-specific trajectories of EFs, suggesting that future study should undertake the analysis of individual development before data-aggregation or generalization from aggregate statistics to individuals.