- Developmental aspects of number concepts were evaluated using participants from the beginning and end of first grade (6–7 years old), third and fifth grades (7–11 years old), and university (22 years old). Participants evaluated the numerical value or physical size of stimuli varying along both dimensions. The numerical distance effect appeared in all groups. In contrast, the size congruity effect started to appear only at the end of first grade. Based on our results, a model of internal representation of magnitude claiming that there are two different representations was propose. At the beginning of first grade children can automatically access only one of these representations and only from the end of first grade can they access both of these representations.