The current chapter presents the findings of a study regarding the development of the mathematical representation of magnitude in older preschool children. While the teaching content was identical across groups (the concept of magnitude as it pertains to length, area and volume was taught by the identification of different sizes and measurements), the types of sign/symbol mediation used in the lessons (signs, models and symbols) varied. All experimental groups demonstrated higher effectiveness in acquiring the concept of magnitude compared to the control group, where no lessons were conducted. However, the group relying primarily on models proved to be the least effective. Further analysis indicated that this outcome was moderated by children’s levels of executive function: those with low or medium levels of self-regulation experienced greater difficulty in mastering model-based programm. In conclusion, teaching content was found to be a significant predictor of the effectiveness of the learning of elementary mathematical concepts, but the type of mediation used in lessons depended on, and should be selected considering, the level of the development of executive function and self-regulation in older preschool children.