The comorbidity of ADHD and reading difficulties (ADHD + RD) is believed to be a disability distinct from ADHD alone, with unique challenges faced by individuals suffering from one disability versus the other. We aimed to examine the differential effect of 8 weeks of cognitive training on reading abilities and on executive functions, through use of the Wisconsin task, in children with ADHD and in children with ADHD + RD. Greater impairments in reading and executive functions, especially in speed of processing, were found in the comorbid group at baseline. The comorbid group showed greater improvements in most measures after training as well. We propose that the cognitive training used in the present study affected not only the immediate abilities of executive functioning but also the secondary ability of reading, especially in the comorbid group, by improving in particular, speed of processing. We suggest that a differential approach should be taken when treating children with ADHD + RD versus treating ADHD children.