Few neuropsychological measurement tools of attention can assess preschoolers despite adequate instruments’ potential to facilitate early diagnostic processes, which are currently demanding. This study’s objective was to evaluate the QbMini, an attention-deficit hyperactive disorder (ADHD) measurement tool for preschoolers. QbMini performances of 37 5-year-old ADHD patients, 55 healthy controls, and 26 children with specific language impairment (SLI) were compared using univariate analyses of variance. The test’s predictive power was evaluated using receiver operating characteristics (ROC) analyses and compared to a parental rating scale. Finally, the scales were compared by correlating their respective scores. The QbMini measures ADHD symptoms and reliably differentiates between healthy children and patients, but not between children with ADHD and children with SLI. The QbMini can indicate presence and strength of ADHD symptoms, but fails to diagnose ADHD. It measures symptoms in a different way than parental ratings and might be stronger in distinguishing between hyperactivity and inattention.