Neurocognitive testing is a critical tool in the management of sport-related concussions. Adversity during childhood and adolescence affects cognitive tasks, behavioral outcomes, and academic performance. Adversity may be important in baseline concussion test validity as well; however, the influence of these experiences is not well understood. To examine the relationship between individual-level experiences of adversity and baseline test validity of Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT). We hypothesized that experiences of poverty, maltreatment, or extreme neighborhood deprivation would be associated with lower odds of baseline test validity. Case-control study. Cuyahoga County, Ohio. A total of 6495 student-athletes born from 1995 through 2005 who completed a baseline ImPACT test between 10 and 18 years old and were identified in the Child-Household Integrated Longitudinal Data system, a comprehensive data system with demographic and social service usage outcomes for children in Cuyahoga County, Ohio. Baseline concussion test validity was determined using the ImPACT built-in validity measure. Experiences of adversity during the sensitive developmental periods of early childhood and adolescence were key independent variables. Our findings suggested that social mobility may play an important role in baseline validity. Youth with upward social mobility (ie, poverty or neighborhood deprivation in early childhood only) were not different from youth without such experiences (odds ratio [OR] = 0.91, P = .74). Youth with persistent adversity across childhood or downward social mobility (ie, poverty or high neighborhood deprivation in adolescence only) had 50% to 72% lower odds of achieving a valid baseline test (persistent poverty, OR = 0.59, P = .05; adolescent poverty only, OR = 0.50, P = .004; adolescent neighborhood deprivation only, OR = 0.28, P < .001). Maltreatment had no significant effect on test validity. These findings indicated that certain patterns of adversity may predispose youth to invalid baseline testing scores, potentially increasing their risk of inappropriate injury management and poor outcomes.