The aims of the study were to explore the validity of a set of computerized tests, and to explore the validity of reaction time variability as an index of sustained attention. In Phase I, 105 7- to 10- year-old children were presented with five tests from the Neurobehavioral Evaluation System (NES). The children were able to complete four of the tests: the Continuous Performance, Simple Reaction Time, Symbol-Digit Substitution, and Digit Span tests. In Phase II, a follow-up of 88 children, performance on these tests was significantly associated with teacher rating of attention, and with standardized academic achievment measures. Moreover, variability on the Simple Reaction Time, and performance on the Digit Span and Symbol-Digit tests, significantly predicted reading achievement. Similarly, performance on the Digit Span and Symbol-Digit tests significantly predicted mathematics achievement. In addition, variability on the Simple Reaction Time and Digit Span test performance were significant predictors of reading achievement, above and beyond the prediction provided by teacher ratings. (Copyright (c) 1991 The Journal of School Psychology, Inc.)