This chapter discusses mathematics education for students with Intellectual Developmental Disorder, presenting updated definitions according to the American Association on Intellectual and Developmental Disabilities and the American Psychiatric Association. It highlights that the diagnosis involves limitations in intellectual and adaptive functioning, beginning during the developmental period, and that prevalence varies according to socioeconomic context. Furthermore, it analyzes frequent difficulties faced by these students, such as limitations in working memory, abstract reasoning, generalization, attention, and organization, which impact mathematical learning. Even so, the text reinforces that they can learn academic content. Based on systematic reviews and recent studies, the chapter demonstrates the effectiveness of strategies such as explicit instruction, prompting, the use of concrete and virtual manipulatives, visual aids, gestures, task division into intermediate steps, and digital technologies. Individualized interventions have shown improvement in the accuracy, maintenance, and generalization of skills. The chapter concludes that structured practices, with strong visual support and intentional teacher mediation, favor not only operational accuracy but also conceptual understanding, expanding the possibilities for academic and social participation of these students.