This chapter summarizes classical studies on numeracy development and
highlights the impact of children’s own, self-initiated numerical
activities in informal everyday situations on the learning trajectories
toward an advanced number sense. Theories and empirical evidence of the
role early exact and approximate magnitude processing, relational
reasoning, counting, number sequence, and arithmetical skills play in
the development of natural and rational number knowledge are described.
Furthermore, studies on spontaneous focusing on numerosity (SFON) and
spontaneous focusing on quantitative relations (SFOR) are described
arguing that individual differences in self-initiated focusing on
numerosity and quantitative relations explain some of the individual
differences in children’s numerical development during the childhood
years and primary school. Based on this literature review, we claim that
it is important for formal mathematics education to early on take into
account children’s own mathematically relevant activities in both formal
and informal situations.