Executive functions (EF) are closely related to math performance. Little is known, however, about the role of EF in numerical magnitude skills (NS), although these skills are widely acknowledged to be important precursors of math learning. The current study focuses on the different roles of updating, shifting, and inhibition in NS. EF and NS were assessed in 47 five-year old children. Furthermore, 21 children were presented with six training sessions aimed at improving NS. Both pre-test and improvement scores were used to investigate the role of EF in NS. Bayesian analyses show that updating is a more important predictor of individual differences in NS than shifting and inhibition. Moreover, children with better updating skills showed more improvement in number line estimation after the training. It is argued that NS rely on the processing of multiple sources of information and, therefore, may be dependent on updating skills. (Contains 5 tables.)