The aim of our article is to find suitable integrative phenomena for both visual arts and mathematics, with a focus on preserving the nature of each of these subjects and their specific methods of acquiring and processing information. This article builds a picture of how to design and conduct an integrative learning continuum which genuinely preserves the nature of mathematics. To draw conclusions, we combined datasets from mathematics teacher education and the lower secondary school context. We found out that suitable integrative phenomena can relate to concepts shared by each of the integrating disciplines, such as ratio; or they can be typical processes of knowledge acquisition and construction, such as sorting. The teaching experiments revealed that the integrative phenomena appropriate for use in school must enable a joint investigative learning experience. The third finding was that the pupils needed teacher support to view the subjects more broadly.