The paper discusses the possibilities of symbol application to the learning of function concept in primary school. Author differentiates symbol and sign mediation. . Symbolic mediation is divided into productive (which assists transfer to sign mediation) and unproductive. Three groups of children were learning concept of function according to three programs: traditional, based on sign mediation; experimental, based on productive symbolic mediation; experimental, based on unproductive symbolic . mediation. Experiment showed that symbolic mediation could be a productive way of learning concept of function if core relationships in image content of symbol that can bring to sign mediation are defined.