For a modern mathematics education that is strongly oriented towards the individual learning and performance levels of children, fundamentally different structures of learning are required compared to before, both in grade-specific instruction and in mixed-age groups. The new teaching resource Flex and Flo has been developed specifically to address these challenges: the central element for the students' work consists of four thematic booklets per school year, which the children can largely work on independently: two booklets for arithmetic, one for geometry, and one for the area of applied mathematics and measurements. The central element for the teacher is the teacher's guide, which includes detailed instructions, photocopiable templates, and suggestions for further exercises to support individual development. In addition to classroom observation, the diagnostic booklets represent an important tool.