Children with intellectual and developmental disabilities (IDD) experience significant difficulties in attention, learning, executive functions, and behavioral regulation. Emerging evidence suggests that computerized cognitive training may remediate these impairments. In a double blind controlled trial, 76 children with IDD (4–11 years) were randomized to either an attention training (n = 38) or control program (n = 38). Both programs were completed at home over a 5-week period. Outcome measures assessed literacy, numeracy, executive functioning, and behavioral/emotional problems, and were conducted at baseline, post-training, and 3-month follow-up. No training effects were observed at post-training; however, children in the training group showed greater improvements in numeracy skills at the 3-month follow-up. These results suggest that attention training may be beneficial for children with IDD; however, the modest nature of the intervention effects indicate that caution should be taken when interpreting clinical significance.