According to the Centers for Disease Control and Prevention, 300,000 children and teens will suffer a concussion while participating in athletics. 

http://www.wusa9.com/story/news/health/health-alert/2014/07/17/concussions-teens-family-health-tbi/12774929/

Thomas James, WUSA 10:36 p.m. EDT July 18, 2014

A 2010 study by Purdue University and Indiana University published in the Journal of Neurotrauma, “Functionally-Detected Cognitive Impairment in High School Football Players Without Clinically Diagnosed Concussion,” examined the health of 21 players throughout the course of a season. The study focused particularly on 11 of these adolescent/late-teen subjects.

The study’s findings include:

The 21 players experienced 15,264 significant collision events across 48 practices and games (an average of 15.5 collision events per player per organized activity); four of the 21 players were diagnosed with a concussion.

Four of the players with no clinically observable signs of concussion still showed significant functional impairments when observed with MRI technology or verbal/cognitive testing. This suggests that a new category of brain-related injury problem needs to be diagnosed.

- See more at: http://journalistsresource.org/studies/society/education/high-school-football-concussions/#sthash.69WWJjWl.dpuf

How many teens (on average) suffer from concussions?