Enrolled children went through four study phases : 1 ) Screening period ( 4 weeks ) and a 2 day medication washout period ; 2 ) open-label period with dose initiation of MPH-MLR 15mg daily and individual dose optimization treatment period ( 2-4 weeks ) ; 3 ) double-blind crossover period in which participants were randomized to sequences ( 1 week each ) of placebo and the optimized MPH-MLR dose given daily ; and 4 ) follow-up safety call .