Bernhard Matter explores how learning materials can be designed for different age groups and qualitatively examines the common learning situations related to various mathematical topics. In an educational design research project, learning offerings are developed and tested, and learning processes are analyzed. Over a period of three years, interventions on mathematical topics from the content area "Numbers and Operations" are conducted. The understanding of mathematics as a science of interconnected patterns and of mathematics learning as an individual and cooperative construction process enables sustainable mathematics instruction. Building on this foundation, the parallelization of content and the conscious implementation of the spiral principle can positively influence the learning processes in a heterogeneous, mixed-age learning group.