The differences in apparent prevalence of childhood hyperactivity between England and North America are more than 20-fold. This paper seeks to illuminate the reasons for the difference by applying a standard measure [Conners Teacher Rating Scale] to 437 English schoolchildren, aged 6 to 9 years, and comparing them with published surveys from the United States and Australasia. The rating scale had moderate interrater reliability and stability over time; it distinguished between children referred for psychiatric treatment and normal schoolchildren. Component analysis yielded a factor of hyperactivity-inattentiveness, distinct from conduct disorder. The mean hyperactivity scores of English children were higher than in most U.S. surveys but lower than in New Zealand. The national differences in rates of diagnosed hyperactivity are likely to reflect diagnostic inconsistency rather than true differences in children's behavior.