Objective: To test the efficacy and tolerability of the methylphenidate transdermal formulation (MTS) against immediate-release methylphenidate (IR MPH) and placebo in a 12-hr analog classroom setting. Method: A total of nine boys ages 6 to 9 years, medicated with MPH for ADHD, complete a within-subject, double-blind study. For the purpose of the study, the boys are administered a dose of 20 cm[superscript 2] MTS, a matched dose of IR MPH 10 mg TID, and placebo. ADHD symptoms and frequency counts of classroom rule violations and the number of math problems completed are assessed hourly, during three consecutive analog classroom sessions. Results: Findings show that, across measures and throughout the day, both treatments significantly differentiated from placebo (p less than 0.05) but not from each other. It is also observed that the MTS produced more consistent results across the day but had a delayed onset versus IR MPH. Both medications are well tolerated with only mild reductions in sleep onset. Conclusion: The MTS demonstrates comparable efficacy and tolerability to TID IR MPH. (Contains 2 tables and 1 figure.)