Instruments have been used for centuries in mathematical experience and in the teaching tradition as well. One example is cultural instruments inherited from tradition (e.g., rulers, abaci, compasses, curve-drawing devices) that have followed or anticipated the theoretical development of mathematics. In this article, the authors analyze two cases of instruments (the compass and the abacus) which are very commonly found in primary school classes. They do so by inserting them in a Vygotskian framework which allows them to be more precise about the quality of social interactions (individual and group tasks; discussions orchestrated by the teacher), realized under teacher's guidance, used in order to foster the individual construction of mathematical meanings. The two examples concern two artifacts inherited from tradition and describe the shift from the "concrete" instrument to the "mental" one in primary school. The users are young pupils, chosen to emphasize the need of starting quite early to nurture a theoretical attitude toward mathematics.