Storage and/or automatic retrieval of the basic facts of addition from the long-term memory seems to be impaired in children with ADHD presenting arithmetical difficulties. The present study was carried out to evaluate the effectiveness of an educational intervention model designed to teach basic facts of addition as a means of advancing from counting procedures to memory-based processes in 7 children with ADHD, divided into two groups (control and intervention). The main hypothesis was that the explicit teaching of decomposition strategies would lead to an advanced use of a memory-based procedure. It is an experimental study involving the use of a blind, parallel, randomized, controlled clinical trial. The intervention group participated in 10 one-hour sessions over a 10-week period, while the control group received the same quantity and distribution of teaching time. They carried out the kind of activities generally carried out in the classroom. Although there was no apparent statistical difference between the groups, our findings suggest that the tested educational intervention model is effective at promoting the retrieval of memory-based facts, since the intervention group came to predominantly adopt a memory-based strategy. A carefully designed educational program enhances memory-based processes in students with ADHD. These findings have important implications for further research considering interventions for both students with ADHD and those who perform poorly in arithmetic.