This is a phase 2, randomized, multi-center, double-blind, 3-period and 3-treatment crossover study designed to evaluate the safety and duration of efficacy of SPD465 (50 or 75 mg) compared with placebo and an immediate release amphetamine salt formulation (25 mg) in adults with ADHD. The controlled environment used in this study is an analog classroom setting adapted for a 16-hour adult day.