In this classroom a child introduced the word "split" when he was asked to describe his mental activity in performing the addition of two numbers; the teacher initiated a spatial representation using a broken line. Subsequently, the children used their own pictorial representations. The paper presents an analysis of the numerical diagrams used by these fourth graders to represent their "splitting notion." Splitting evolved into a metaphor that fostered the emergence of these children's numerical meanings. Contains 10 references. (Author)