In this 9-week , double-blind , active-controlled study , patients aged 6-17 years with a previous inadequate response to MPH were randomized ( 1:1 ) to dose-optimized LDX ( 30 , 50 or 70 mg/day ) or ATX ( patients < 70 kg : 0.5-1 .2 mg/kg/day , not to exceed 1.4 mg/kg/day ; patients 70 kg : 40 , 80 or 100 mg/day ) .