More U.S. high school students self-report having had a concussion than is reflected in data from hospitals and school systems, according to a new study from the Centers for Disease Control and Prevention. About 15% of participants in the CDC’s latest Youth Risk Behavior Study (YRBS) say they have experienced at least one concussion related to sports or physical activity over a 1-year period. That prevalence, equating to 2.5 million children, is higher than what’s been reported in emergency rooms or reported by athletic personnel. Perhaps even more surprising, 6% of the students reported they had two or more concussions in the same 1-year period. The data suggest a substantial number of cases could have been missed, concludes the CDC. While the numbers were higher for boys than for girls, any student who played a team sport was more likely to experience a concussion than those who did not. The numbers went up when students played more than one sport. The revelations bubbled up through the results of the most recent YRBS, a cross-sectional study of 14,765 public and private school students in grades 9 through 12. Last year’s survey included a question about concussions for the first time. One clear limitation of the study is the fact that it’s designed as a self-reporting mechanism, with no corroboration from healthcare professionals. Still, the results may be a hint that providers need to probe younger patients as needed for previous concussion-like symptoms even in the absence of an “official” diagnosis in the history.