Response to methylphenidate (MPH) in 36 boys (7-12 years) with attention deficit hyperactivity disorder (ADHD) was examined in a double-blind, placebo-controlled, crossover study at the National Centre for Child and Adolescent Psychiatry, Oslo, Norway. Significant improvements in the level of hyperactivity at home or at school and in conduct problems at school were obtained in response to MPH (0.5 mg/kg/day) in 83% (behavior was at normal levels in 60%). Neuropsychological tests showed MPH-induced improvements in sustained attention (Children’s Checking Task [CCT] and Continuous Performance Test [CPT] of vigilance), working memory (Paced Auditory Serial-Addition Task [PASAT]) and motor coordination (Maze test).
Pre-treatment high levels of hyperactivity and inattention, relatively young age, and absence of emotional disorders were correlated significantly with normalization of hyperactive behavior in 71% of cases. Test performance and neurodevelopment scores had no predictive value. 
COMMENT. The degree of hyperactivity in children with ADHD is correlated with response to MPH treatment. This finding in the Oslo study corroborates previous reports, both in clinical and animal studies, showing that subjects with the highest levels of motor activity are most likely to respond positively to MPH, whereas those with lower activity levels are sometimes made worse [2, 3]. In these studies, neuropsychological test performances were also improved, and the occurrence of subtle signs of neurological abnormality was a likely predictor of response to MPH. Taylor et al  have also reported that high levels of motor activity, impaired attention and motor coordination, younger age and absence of emotional problems may predict a response to MPH.
Denney CB and Rapport MD, University of Hawaii, evaluated the validity of models designed to predict MPH-responsiveness in children with ADHD . They concluded that the magnitude of reponse to MPH measured by classroom attention and behavioral inhibition are correlated and predictive of academic performance and teacher-rated behavior.
Comorbid anxiety and ADHD response to MPH. Diamond IR, Tannock R, and Schachar RJ, University of Toronto, examined the effect of comorbid anxiety on response to MPH in ADHD . Contrary to previous reports, behavioral response and side effects with MPH were unaffected by comorbid anxiety after 4 months of treatment, titrated to a dose of 0.7 mg/kg. Difficulties in measurement of childhood anxiety may account in part for differences in results.