This book is aimed at teachers, educational staff in preschool and school settings, students of special education, and interested parents. It provides a comprehensible introduction to the theoretical foundations of mathematical thinking, with particular attention to the specific needs of students with intellectual disabilities. In addition to the development of mathematical competencies within a developmental stage model based on the theory of J. Piaget, there is a brief insight into the structure- and level-oriented approach of the renowned mathematician R. Kutzer and its application possibilities for one's own teaching. The explanations are vividly complemented by illustrations and images, making it a valuable resource for non-specialist teachers in selecting planning and design.