Placebo-Controlled Comparison of Two Different Brands of Modified-Release Oral Dosage Forms Regarding Safety and Efficacy in Children With Attention Deficit Hyperactivity Disorder (ADHD) Aged 6 - 14

Inclusion Criteria: Patients who meet all of the following inclusion criteria will be eligible for enrollment in the study: * Male and female patients aged 6-14. * Patients having a diagnosis of ADHD of any type according to DSM-IV criteria, as established by history, psychiatric examination and a structured diagnostic interview (Kiddie-Sads-Present and Lifetime Version) * Patients, whose symptoms are adequately controlled by a stable and well-tolerated dose of a immediate release methylphenidate equivalent of 20mg for one month before screening. Exclusion Criteria: * Patients with comorbid psychiatric conditions with symptoms requiring current pharmacological treatment (e.g. major depression, psychosis). * Patients who are taking any concomitant medications likely to interfere with the study drug or confound efficacy or safety assessments, e.g. * Tricyclic antidepressants, buproprion, clonidine, buspirone 2 weeks before randomization. * Atomoxetine 2 weeks before randomization. * Fluoxetine or antipsychotics 1 month before randomization. * Pemoline and amphetamines 1 week before randomization. * Patients with a known non-response to methylphenidate. Other protocol-defined exclusion criteria may apply.