David Ball, a professor of risk management at Middlesex University, analyzed U.K. injury statistics and found that as in the U.S., there was no clear trend over time. “The advent of all these special surfaces for playgrounds has contributed very little, if anything at all, to the safety of children,” he told me. Ball has found some evidence that long-bone injuries, which are far more common than head injuries, are actually increasing. The best theory for that is “risk compensation”—kids don’t worry as much about falling on rubber, so they’re not as careful, and end up hurting themselves more often.