The degree of academic achievement following early onset brain injury is poorly understood. Furthermore, it is unclear if academic success can be predicted by age of onset or other lesion variables (e.g., size, laterality). The purpose of the current study was to describe patterns of academic achievement in individuals with childhood-onset focal brain lesions and to determine the role of variables in the plasticity or vulnerability of the developing brain with regard to achievement. Academic achievement data were collected from 58 individuals with childhood-onset focal brain lesions. The participants' reading, spelling, and arithmetic scores, as measured by the Wide Range Achievement Test, were analyzed in relation to several neuroanatomical variables, including lesion laterality, lesion site, and lesion size. The relationship between achievement and gender, age of onset, etiology, age at testing, and time since lesion onset was also identified. As a group, achievement scores did not differ from normative data, and the majority of the sample demonstrated adequate skills in each domain. However, the frequency of deficits was larger than expected when compared to base rates, suggesting vulnerability to early insult. Achievement scores were correlated with intelligence scores, but did not differ based on lesion laterality, lesion site, age of onset, or etiology. Size of lesion was significantly correlated with reading and spelling but not with arithmetic outcomes. Gender differences were identified, with males performing significantly better on the arithmetic measure than females. The age of onset, age at testing, and time since lesion onset were not correlated with achievement scores in any domain. No interactions were found between lesion laterality and gender or lesion site and lesion laterality. An interaction between gender and lesion site was found, but the significance of the finding is unclear. The current findings provide mixed evidence for the plasticity-vulnerability debate, as many individuals were able to achieve adequate academic skills whereas others demonstrated significant impairments. Further research is needed to elucidate factors that may predict achievement outcomes in individuals with childhood-onset focal brain injury.