Attention-deficit hyperactivity disorder (ADHD) is a heavily studied topic in neuropsychology and general psychology, psychiatry, and pediatrics. The Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition, Text Revision (DSM-IV) is used to diagnose ADHD, but its criteria are behaviorally defined, while ADHD is a neurological dysfunction. The DSM-IV diagnostic criteria do not differentiate between attention and inhibition or executive functions (EF). As well, there is little agreement in the field about what constitutes ADHD and EFs or how to measure or diagnose them, let alone rule them out. When rendering an ADHD diagnosis, the responsible clinician considers DSM-IV criteria along with other reasons why an individual may express symptoms of ADHD, for reasons other than ADHD. This article discusses postulated mechanisms of action for some medications prescribed for ADHD, the variance of medication outcomes in research, the variance of assessment measures used in identifying ADHD subjects for research, and flaws with DSM-IV-based diagnosis. An argument is posed that the field of neuropsychology needs a cohesive and agreed-upon definition of ADHD and EF and how to measure it to more exactly research the topic, accurately diagnose the disorder, and assist prescribing professionals to use medications with improved first-trial precision.