If an examinee exerts inadequate effort to perform well during a psychological or neuropsychological exam, the resulting data will represent an inaccurate representation of the individual's true abilities and difficulties. In adult populations, methodologies to identify noncredible effort have grown exponentially in the last 2 decades. Though a comparatively modest amount of work has focused on tools to identify noncredible effort in pediatric populations, recent research has demonstrated that children can consistently pass several stand-alone symptom validity tests (SVTs) using cutoffs established with adults. However, no identified studies have examined the implications of pediatric SVT failure for ability-based test performance. The current sample consisted of 276 children aged 8–16 years referred consecutively for outpatient clinical neuropsychological consultation following mild traumatic brain injury (TBI). An earlier subgroup of this same case series that also included 17-year-olds was presented in Kirkwood and Kirk (2010). Nineteen percent of the current sample performed below the actuarial cutoff on the Medical Symptom Validity Test (MSVT). No background or injury-related variable differentiated those who passed from those who failed the MSVT. Performance on the MSVT was correlated significantly with performance on all ability-based tests and explained 38% of the total ability-based test variance. Participants failing the MSVT performed significantly worse on nearly all neuropsychological tests, with large effect sizes apparent across most tests. The results provide compelling evidence that practitioners should add objective SVTs to the evaluation of school-aged youth, even when secondary gain issues might not be readily apparent and particularly following mild TBI.