Objective: Compare observed and forecasted efficacy of mixed amphetamine salts extended release (MAS-XR; Adderall) with atomoxetine (Strattera) in ADHD children. Method: The authors analyze data from a randomized, double-blind, multicenter, parallel-group, forced-dose-escalation laboratory school study of children ages 6 to 12 with ADHD combined or hyperactive/impulsive type. Primary efficacy measures are attention and deportment scores on the SKAMP behavioral rating scale, and secondary efficacy measures are academic performance scores from the PERMP test. Results: MAS-XR elicits greater improvements than atomoxetine in each domain within 3 weeks of treatment, including attention, number of math problems attempted and correct, and overall clinical functioning. Treatment differences in each outcome measure at subsequent weeks are projected from generalized estimating equations to become greater with the duration of extension of the treatment regimen. Conclusion: This study suggests that relative advantages of MAS-XR seen in the first 3 weeks are likely to be maintained in subsequent weeks. (Contains 4 tables and 6 figures.)