**Abstract**

Focusing on diagnosis and support of basic mathematical competencies is not only important for learning mathematics in general but also especially relevant for students with mathematical learning difficulties. Fostering basic mathematical competencies, like understanding numbers and operations as well as place value, is a central objective of the project "MaCo" (Catching up in Mathematics after Covid), which will be presented in this chapter. The project itself addresses both, teachers and students, and, not least, tries to meet central challenges after the Covid pandemic. The developmental research and research activities in this project were guided by a design-based research approach. Exemplary for the project, developed concepts and materials for understanding place value in inclusive settings on primary level are illustrated, completed by first evaluations. On the one hand, these concepts and materials comprise concrete activities and tasks, explanatory videos, and web applications designed for students. On the other hand, the professionalization of teachers and facilitators is pursued by massive open online courses, materials for professional development programs, and accompanying didactic manuals for students' materials.

**Keywords:** inclusive mathematics, teacher professionalization, learning difficulties, digital learning materials, place value
