The present study investigated the predictive role of spatial skills for arithmetic and number line estimation in kindergarten children (N = 125). Spatial skills are known to be related to mathematical development, but due to the construct's non-unitary nature, different aspects of spatial skills need to be differentiated. In the present study, a spatial orientation task, a spatial visualization task and visuo-motor integration task were administered to assess three different aspects of spatial skills. Furthermore, we assessed counting abilities, knowledge of Arabic numerals, quantitative knowledge, as well as verbal working memory and verbal intelligence in kindergarten. Four months later, the same children performed an arithmetic and a number line estimation task to evaluate how the abilities measured at Time 1 predicted early mathematics outcomes. Hierarchical regression analysis revealed that children's performance in arithmetic was predicted by their performance on the spatial orientation and visuo-motor integration task, as well as their knowledge of the Arabic numerals. Performance in number line estimation was significantly predicted by the children's spatial orientation performance. Our findings emphasize the role of spatial skills, notably spatial orientation, in mathematical development. The relation between spatial orientation and arithmetic was partially mediated by the number line estimation task. Our results further show that some aspects of spatial skills might be more predictive of mathematical development than others, underlining the importance to differentiate within the construct of spatial skills when it comes to understanding numerical development.Keywords: spatial skills, early mathematics development, kindergarten, arithmetic, number line estimation Journal of Numerical Cognition, 2017, Vol. 3(2), 309-343, doi:10.5964/jnc.v3i2.36 Received: 2016-04-25. Accepted: 2017-02-14. Published (VoR): 2017 Handling Editors: Silke Goebel, University of York, York, United Kingdom; André Knops, Humboldt-Universität Berlin, Berlin, Germany; Hans-Christoph Nuerk, Universität Tübingen, Tübingen, Germany *Corresponding author at: University of Luxembourg -Campus Belval, Maison des Sciences Humaines, 11, Porte des Sciences, L-4366 Esch-Belval. Email: veronique.cornu@uni.lu This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License, CC BY 4.0 (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.The acquisition of early numerical abilities in kindergarten is important for later mathematical learning, school achievement and more general life outcomes such as adult socioeconomic status (Ritchie & Bates, 2013).School entry mathematical skills are strongly predictive of later academic achievement, resulting in a need to gain a more profound understanding of the processes and cognitive abilities underlying early mathematical d...