An attempt was made in the present study to identify mothers' and caregivers' teaching (mediation) behaviour in relation to toddlers' social behaviour. Participants were 103 toddlers, two- to four-year olds, their mothers, and 28 caregivers at 16 public daycare centres in Israel. Two observations were carried out, one in toddlers' homes and the other in the daycare centres. Research findings indicate that mothers' and caregivers' social mediation behaviour "encouraging" and "regulating behaviour" were related to more prosocial behaviour and to less aggressive behaviour of toddlers. Especially, interesting findings were noted regarding effects of incompatible mediation on children's social behaviour. It was found that when mothers or caregivers exhibited more mediation that was unmatched or unsynchronised with their child's behaviour (i.e. "unspecified encouragement"), their children exhibited more aggressive and less prosocial behaviour.