Currently, there is no objective way to determine whether a person who is diagnosed with Attention Deficit Hyperactivity Disorder (ADHD) can better learn on than off stimulant medication. In the current study 3 adults with ADHD, who had reported that they benefited from stimulant medication (Adderall/d and l- amphetamine or Ritalin/methylphenidate), were either on or off medication, for 30 sessions of an alternating treatments design, as they completed a learning task: the Incremental Repeated Acquisition (IRA) procedure. IRA requires participants to depress numeric keys in a given sequence to produce reinforcement. If participants can press N keys correctly, then they are required to next press N+1 keys. Importantly, from session-to session, the sequence varies. In this way the IRA procedure assesses learning. This research tested whether learning as measured with the IRA procedure was sensitive to the medication at the level of the individual participant. Various measures of learning were explored but only one measure, latency to complete a chain, appeared to be affected by medication, and then only for one participant. Because the effect occurred during the later sessions, future researchers should consider conducting more sessions. More importantly, conducting sessions that exceed 20 min may enhance the IRA procedure's sensitivity. Although the procedure was rather insensitive to medication, inspection of the data, from session-to-session, often revealed smooth curves, despite the changing sequences. These findings suggest that the IRA procedure is a promising tool for evaluating the effects of stimulant medications.