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Acknowledgments: We are extremely grateful to the authors of the studies included in the cost-effectiveness analysis for providing detailed data on the program costs and discussions on ways to most appropriately calculate cost-effectiveness, the J-PAL policy team, three anonymous referees, and B. Nordgren for designing Fig. 1. 10.1126/science.1235350 REVIEW Understanding Neurocognitive Developmental Disorders Can Improve Education for All Brian Butterworth 1,2,3 * and Yulia Kovas 3,4,5 Specific learning disabilities (SLDs) are estimated to affect up to 10% of the population, and they co-occur far more often than would be expected, given their prevalences. We need to understand the complex etiology of SLDs and their co-occurrences in order to underpin the training of teachers, school psychologists, and clinicians, so that they can reliably recognize SLDs and optimize the learning contexts for individual learners. I n the not-too-distant past, children who were unable to learn the usual school subjects to a normal level were classified as having mental retardation, or what we would now call “intel- lectual disability” (U.S.) or “learning disability” (UK). These labels are still sometimes applied to children with severe delays in learning to read and spell, whom we would now call dyslexic, or those with serious social difficulties, whom we would now call autistic (1). Extensive research in cognitive development shows that children with normal or even supe- rior IQs, and who clearly are not mentally re- tarded, can fail to reach acceptable standards in key curriculum areas, such as literacy (2) and numeracy (3). The terms intellectual or learning disability are currently reserved for those whose score on an IQ test is below 70 (the lowest 2%, approximately). The evidence outlined in this Review presents multiple reasons why it is difficult to define neu- rocognitive developmental disorders. Complex ge- netic, brain, and cognitive processes underlying these conditions remain poorly understood. 1 Institute of Cognitive Neuroscience, University College London, Alexandra House, 17 Queen Square, London WC1N 3AR, UK. 2 IRCCS Ospedale San Camillo, Venice, Italy. 3 Melbourne School of Psychological Sciences, University of Melbourne, Melbourne, Australia. 4 Department of Psychology, Tomsk State University, Tomsk, Russia. 5 Department of Psychology, Goldsmiths, University of London, London, UK. 6 Social, Genetic and Developmental Psychiatry Centre, King’s College London, London, UK. *Corresponding author. E-mail: b.butterworth@ucl.ac.uk 19 APRIL 2013 VOL 340 SCIENCE www.sciencemag.org 300