In addition to taking a detailed concussion history, asking an athlete about the number and severity of post-concussion signs or symptoms  and conducting a neurological examination, both during a pre-participation physical evaluation (PPE) , it is critically important for your child's treatment of and recovery from a suspected concussion to provide the treating health care professional with as much information as possible about all prior concussions, including severity of impact and duration of symptoms.
Because many athletes, particularly children under the age of 13 - for whom the most recent international consensus of concussion experts  recommends asking a different set of questions than older athletes, including questions directed to their parents  - do not recognize all the concussions they may have suffered in the past, a structured concussion history should therefore "include specific questions as to previous symptoms of concussion and length of recovery, not just the perceived number of concussions." 
While some research suggests that those with prior concussions do not necessarily suffer more neurocognitive impairment following a re-injury, [1,15] other studies have found that athletes who have suffered multiple concussons are at increased risk for subsequent concussion and more likely to develop persistent post-concussion signs or symptoms , including depression , which require careful management and may have life-long health consequences . A 2009 study  of high school soccer players, for example, found that athletes with a reported history of concussions performed significantly worse on tests of memory, visual processing and reaction time using the ImPACT computerized neurocognitive test battery than those who reported no prior concussion
Under the consensus statement issued after the 4th International Conference on Concussion in Sport in Zurich in November 2012  frequency (repeated concussions over time), concussions close together in time, recent concussion or traumatic brain injury, and repeated concussions occurring with progressively less impact force or slower recovery after each successive concussion are considered important "modifying factors"  in concussion management which may, in some cases, predict the potential for prolonged or persistent symptoms that may lead to a diagnosis of post-concussion syndrome .
The importance of finding out about concussion history is underscored by studies showing that a significant percentage of athletes, especially in contact sports like football, suffer multiple concussions over the course of their athletic career, many of which, for a variety of reasons, go unreported: [11,12,13]
1. Colvin AC, Mullen J, Lovell MR, West RV, Collins MW, Groh M. The Role of Concussion History and Gender in Recovery from Soccer-Related Concussion. Am. J. Sports Med. 2009; 37(9): 1699-1704.
2. McCrory P. et al. Consensus statement on concussion in sport: the 4th International Conference on Concussion in Sport held in Zurich, November 2012. Br. J. Sports Med. 2013; 47:250-258.
3. Castile L, Collins CL, McIlvain NM, Comstock RD. The epidemiology of new versus recurrent sports concussions among high school athletes, 2005-2010. Br. J. Sports Med 2012; 46:603-610.
4. Marar M, McIlvain NM, Fields SK, Comstock RD. Epidemiology of concussions among United States high school athletes in 20 sports. Am J Sports Med 2012;40:747-755.
5. Gissel LM, Fields SK, Collins CL, Dick RW, Comstock RD. Concussions among United States high school and collegiate athletes. J Ath. Training 2007; 42(4): 495-503.
6. Collins MW, Lovell MR, Iverson GL, Cantu RC, Maroon JC, Field M. Cumulative effects of concussion in high school athletes. Neursurgery. 2002;51(5):1175-1181.
7. Moser RS, Schatz P, Jordan B. Prolonged effects of concussion in high school athletes. Neurosurgery 2005;57:300-306.
8. Schatz P, Moser RS, Covassin T, Karpf R. Early Indicators of Enduring Symptoms in High School Athletes with Multiple Previous Concussions. Neurosurgery 2011: 000 (in process).
9. Emery CA, Kang J, Schneider KJ, Meeuwisse WH. Risk of injury and concussion associated with team performance and penalty minutes in competitive youth ice hockey. Br J Sports Med 2011;45:1289-1293.
10. Schulz MR, Marshall SW, Mueller FO, Yang J, Weaver NL, Kalsbeek WD, et al. Incidence and risk factors for concussion in high school athletes in high school athletes, North Carolina, 1996-1999. Am J Epidemiol 2004;160:937-944.
11. McCrea M, Hammeke T, Olsen G, Leo P, Guskiewicz K. Unreported concussion in high school football players: implication for prevention. Clin J Sport Med 2004;14:13-17.
12. Echlin PS, Tator CH, Cusimano MD, Cantu RC, Taunton JE, Upshur RE, et al. A prospective study of physician-observed concussions during junior ice hockey teams: implications for sports concussion education. Neurosurg Focus 2010;29(5):E4.
13. Echlin PS, Skpelja EN, Worsley R, Dadachanji SB, et al. A prospective study of physician-observed concussion during a varsity university ice hockey season: incidence and neuropsychological changes. Part 2 of 4. Neurosurg Focus 2012;33(6):E2.
15. Brooks BL, McKay CD, Mrazik M, Barlow KM, Meeuwisse WH, Emery CA. Subjective, but not Objective, Lingering Effects of Multiple Past Concussions in Adolescents. J Neurotrauma 2013;30:1469-1475.
Most recently revised and updated October 29, 2013