This study examines the effects of a working memory (WM) sensitive math intervention in students with learning disabilities (LD). The intervention aims to improve early mathematical competencies while accounting for weak cognitive resources through a reduced instructional design. These principles are considered to be effective for learning. Ten students with mild to moderate intelligence impairment participated in our study. We applied an AB single-case intervention study across participants to evaluate the effects of the intervention. The students take part in at least 10 30-minute intervention sessions. Non-overlap indices, as well as regression analysis, support positive effects on students' mathematical competencies. Nevertheless, there are still students for whom the effects were unstable or failed to materialize. Besides the effectiveness of the WM-sensitive math intervention, the results support the assumption that the mathematical learning of students with LD is similar to that of students without LD but delayed.