Number representations are long known to be spatially coded. It is assumed that these spatial number representations are foundational for the development of mathematical skill. Yet, crucial evidence for this hypothesis is missing. 1/ It is not known whether it is long term memory or working memory that drives the spatial associations; 2/ There is no conclusive evidence yet that spatial number representations are a scaffold for more complex forms of mathematical ability; 3/ it is unclear how general spatial skills play a role in the construction of spatial number representations and their use in mathematical activities. Moreover, it is possible that the relationship between spatial number representations, spatial skills and mathematical abilities dynamically change with development. The present project proposes to answer these outstanding questions by a large-scale developmental project that measures spatial number representations, spatial skills and mathematical abilities and specifies their relationship over a time window that covers the whole period of formal education, from kindergarten to higher education. Three workpackages will focus on three consecutive levels of education, including the transition to the next level: WP1 kindergarten with transition to primary school, WP2 primary school with transition to secondary school and WP3 secondary school with transition to higher education.