Using the 2007 Health Survey for England, we examine whether knowledge of guidelines is linked to physical activity levels for 1,954 children aged 11-15, and the correlates of adhering to the guidelines. For girls, knowing the guidelines was associated with meeting them, but was weak among boys, for whom only white ethnicity was associated with meeting the guidelines. For girls, being younger, white, and from a manual social class background was associated with meeting the guidelines. Findings support the call for physical activity-promoting policy and programs aimed at specific groups of children who are prone to lower levels of activity.