General cognitive and specific number abilities that underlay arithmetic performance have been heavily investigated among typically developing students; however, the inquiry has rarely been applied to students with mild intellectual disability (MID). We examined whether domain-general cognitive abilities (i.e. working memory, processing speed, and long-term memory) and specific number skills (i.e. approximate and exact numerical systems) are related to arithmetic performance in 93 students with MID (mental age of 7.1 to 8.9 years) and if these relationships are similar to the ones found in 113 typically developing students with the same mental age. The results of our regression models indicated that, in both groups, the three general cognitive abilities independently explained the variance in arithmetic performance when entered in one step; however, none of them had an independent contribution to arithmetic skill in the presence of the specific number abilities. These findings supported those of Von Aster and Shale's developmental model of mathematical cognition and reinforced the notion that specific number abilities constitute the basis for arithmetic skill, and it is possible with the support of the general cognitive abilities among both students with MID and typically developing students.