Individual differences in arithmetic have been explained by differences in cognitive processes and by arithmetic strategy use and selection. In the present study, we investigated the involvement of reactive and proactive control processes. We explored how variation in proactive and reactive control was related to individual differences in strategy selection. We correlated proactive and reactive measures obtained from the AX-CPT and an adjusted N-back task with a measure of strategy adaptiveness during a numerosity judgment task. The results showed that both measures of reactive control (of the AX-CPT and N-back task) correlated positively with strategy adaptiveness, while proactive control was not. This suggests that both cognitive control modes might have a different effect on adaptive strategy selection, where adaptive strategy selection seems to benefit from a transient (late) control mode, reactive control. We discuss these results in the light of the Dual Mechanisms Framework. The last decade has witnessed an increased interest in individual differences in arithmetic (see Cappelletti & Fias, 2016or De Smedt, Noël, Gilmore, & Ansari, 2013 for an overview). Generally, the selection and use of appropriate arithmetical strategies explain part of this variability Imbo, Vandierendonck, & Rosseel, 2007). In the present study, we investigated the involvement of reactive and proactive control processes in this selection of appropriate strategies. Recently, the involvement of cognitive control processes in arithmetic strategy use has been investigated (for a review, see and sometimes interpreted as reflecting either reactive or proactive control. However, the specific involvement of these control processes was never explicitly investigated, which was the aim of the current study. Because strategy selection involves a decision-making process (i.e., choosing between the different strategies), cognitive control is involved to make an adaptive strategy selection. Investigating how proactive and reactive control are involved in the process of strategy selection, furthers our understanding on arithmetic strategy use.To adequately perform mental arithmetic, a variety of cognitive processes are needed. Among these processes, we consider attention (e.g., focus on the arithmetic problem; Menon, 2010), working memory (e.g., holding and manipulating information in mind; Andersson, 2008;Raghubar, Barnes, & Hecht, 2010), response selection, Journal of Numerical Cognition jnc.psychopen.eu | 2363-8761 and executive functions. Miyake et al. (2000) identified three different functions in executive control and all three are known to contribute to individual differences in arithmetic: (a) shifting between tasks or mental sets (Yeniad, Malda, Mesman, van IJzendoorn, & Pieper, 2013), (b) information updating and monitoring of working memory representations (Raghubar, Barnes, & Hecht, 2010), and (c) inhibition of prepotent or dominant responses (Bull & Scerif, 2001;Gilmore et al., 2013;Kroesbergen, Van Luit, Van Lieshout, Van Loos...