“…Before their first birthday infants can coordinate their own actions with those of a social partner in familiar routines and cooperative social games, such as passing a ball to and fro, in which infants’ actions are the same as their social partner (Duncan & Farley, 1990; Hubley & Trevarthen, 1979; Ross & Lollis, 1987). In the second and third years of their postnatal lives, children become skilled collaborative partners in novel and more complex collaborative exchanges in which infants’ actions are complementary to those of their social partner, such as working together to retrieve a toy from a puzzle box (Ashley & Tomasello, 1998; Brenner, & Mueller, 1982; Brownell & Carriger, 1990; Brownell, Ramani & Zerwas, 2006; Warneken, Chen, & Tomasello, 2006; Warneken & Tomasello, 2007). Importantly, engagement in collaborative activities plays a critical role in children's development by supporting their event memory (Sommerville & Hammond, 2007), planning and problem-solving skills (Azmitia, 1998; Radziszewska & Rogoff, 1988), and learning of culturally specified behaviours (Rogoff, 1990; Tomasello, 2009).…”