“…Its roots can be found in the seminal work of Krutetskii (1976) and Wertheimer (1959), and for years it has been considered an important element of adaptive expertise (Baroody & Dowker, 2003;Hatano & Inagaki, 1986). More recently, it has received significant attention from European researchers, who have been interested in children's flexibility with arithmetic (Blöte, Klein, & Beishuizen, 2000;Blöte, Van der Burg, & Klein, 2001;Klein, Beishuizen, & Treffers, 1998;Torbeyns, Verschaffel, & Ghesquiere, 2006;Verschaffel, Luwel, Torbeyns, & Van Dooren, 2007). Perhaps because of these varying interests, definitions of flexibility have also varied.…”