Diagnosing attention deficit/hyperactivity disorder (ADHD) in children and young people typically relies on clinical observation and subjective parent, teacher and self-reports. The subjective nature of reports combined with contradictory or missing data can result in diagnostic uncertainty and delay. The aim of this study was to assess whether the addition of an objective test of attention, impulsivity and activity (QbTest) as an adjunct to standard ADHD assessment could accelerate the diagnostic process in routine National Health Service (NHS) settings. In a pre vs. post-test audit design, case records were examined in 40 cases diagnosed without the QbTest [pre-QbTest group] and 40 cases diagnosed with the QbTest [QbTest group], recording the number of consultations until a confirmed ADHD diagnosis was reached. Using Poisson regression, significantly fewer clinician consultations (mean 2.18 vs. 3.05; p < .02) were required to confirm the diagnosis of ADHD when the QbTest was used to augment assessment in comparison to standard assessment as usual. The findings suggest that the addition of the QbTest to standard clinical assessment may reduce time to diagnosis and potentially result in cost savings to the NHS. These preliminary data suggest that there is a potentially clinically meaningful benefit of adding the QbTest to routine clinical ADHD assessment and this should be examined next in the context of a randomised controlled trial.