- Study end point classification: NA The investigators plan to use a randomized double-blind placebo-controlled crossover (DBPC) design. Children will be tested twice (once after the administration of the optimal dose of LDX and once after placebo) with a computer-based behavioral paradigm which measures efficient arousal modification in response to changing environmental settings. The investigators will use a Go/No-Go task with 4 different ERs (1 secs, 2secs, 4secs, 8secs). If children see an upright triangle (Go stimulus) they have to respond; if children see an inverted triangle (No-Go stimulus) they must withhold responding.