Attention-Deficit/Hyperactivity Disorder (ADHD) is associated with diminished neuropsychological functioning. This randomized, double-blind, placebo controlled, study is the first comparison of two extended release stimulant-based medications (Adderall XR and Concerta) and placebo on ADHD neuropsychological functioning. Adolescents diagnosed with ADHD (n=35, 19 males) completed three separate assessments (5, 8, 11 p.m.) on three different days and medications (Concerta, Adderall XR and Placebo). The assessments consisted of two different neuropsychological tests, the Delayed Matching-to-Sample and the Go/No-go (GNG), which measure visual memory, attention span, and response inhibition. Results indicated a significant effect of medication on signs of impulsivity and memory. Simple contrasts showed significant improvement in neuropsychological functioning (as measured by commission errors, reaction time, and recall accuracy) when participants were taking Concerta as opposed to placebo. These results suggest that Concerta impacts not only symptomatic behaviors but also cognitive functioning, which has implications for both academic performance and daily functioning.