The purpose of this study was to identify the most common causes of head injury and associated symptoms of concussion in a population of school children (n=1,372,979). Using standardized injury report forms, we identified the mechanisms of head injury associated with various sports/recreation activities and assessed each injury for the presence of concussion symptoms. Head injury reports (n=7,765) were coded using the WHO's ICECI and ICD-10 E-codes. 1,338 Cases reported symptoms of concussion. The majority of head injuries occurred during School Free-Play/Recess (59.8%). Combative Sports and Wheeled Non-Motored Sports were the activities most often associated with concussion symptoms (rate of concussion (RC): 48.3% and 44.4%, respectively, p<0.001). School Free-Play/Recess and Physical Education Classes were significantly less likely to have head injuries associated with concussion (RC: 16.0%, p<0.001, and 12.4%, p=0.034, respectively). The most common causes of head injury were (1) Struck by an Object (24.9%) and (2) Falling on the Same Level (22.8%). Falling from a Transport was the only etiological code significantly associated with concussion symptoms after head injury (RC: 28.7%, p<.001). Results were similar when using the two coding structures in combination. Prevention efforts should focus on activities where children are moving at high speeds since these are more likely to cause a concussion when a head injury occurs.