The aim of this study is to describe what kind of knowledge base is needed when pre-school teachers work goal-oriented with children's mathematical learning. The question of this study aims to answer is: What kind of knowledge base do pre-school teachers need when they work with the object of learning in the pre-school context? Both as a theoretical and an analytical framework, we use variation theory. In all, four pre-school teachers are involved in the study. The research results indicate that it is important for pre-school teachers to have subject and pedagogical content knowledge in order to recognize children's experiences and be aware of their expressions. (Contains 3 figures and 1 footnote.)