Headsprout Early Reading is a computer-based program designed on behavioral principles to enhance the basic skills that underpin the initial development of reading. In a within and between groups design, and using primary schools within Northern Ireland that had a currently high proportion of disadvantaged pupils, children who were behind their peers in progress with reading were randomly allocated to an intervention group (n = 79), where the target was to work through 80 reading training episodes within a school year, or a teaching as usual group (n = 44). Reading skills were assessed in all children before, at the midpoint, and after the intervention using a flashcard-based phonics identification test with three levels of difficulty, and before and after intervention using a standardized reading assessment, which generated a sentence reading age and a phonics reading age. Both groups showed increased scores on all measures over the 6 months of the study, but the intervention group showed markedly greater improvement. Importantly, the mean scores on sentence reading age and phonics reading age for the intervention group increased by over 17 months and 12.1 months, respectively, as opposed to 7.6 months and 7.8 months with the control group. These findings also validated the use of the flashcard-based phonics identification test with this population. This study indicates that widespread use of Headsprout Early Reading in mainstream education could be highly effective.