We are not well informed regarding the ability-achievement relationship for twice-exceptional individuals (very high cognitive ability and a diagnosed disability, e.g., autism spectrum disorder [ASD]). The research question for this investigation (N = 59) focused on the predictability of achievement among variables related to ability and education in a twice-exceptional sample of students (cognitive ability of 120 [91st percentile], or above, and diagnosed with ASD). We determined that WISC-IV Working Memory and Processing Speed Indices were both significantly positively correlated with achievement in math, reading, and written language. WISC Perceptual Reasoning Index was uniquely predictive of Oral Language test scores. Unexpected findings were that ASD diagnosis, Verbal Comprehension Index, and forms of academic acceleration were not related to the dependent variables.