Toy sharing and sibling interaction are major contexts for young children's developing social skills. This study examined the effects of parenting on sharing between siblings, and the effectiveness of a 5-session parenting programme in promoting sharing. Forty-eight mothers with two preschoolers participated. Each family was assessed before and after the parenting programme and at a 6-week follow-up. The mother completed measures of her parenting approach and reported on her children's behavior. The children were interviewed to obtain cognitive measures. Interactions of the mother and two children were observed in a laboratory playroom. Fathers and preschool teachers also reported on the children's behavior. Two parts of the study used data collected at the first assessment. First, multivariate analyses showed significant correlations between mother behaviors and those of the children, and between the two children. Second, the immediate effects of parenting on children's sharing were explored by manipulating the mother's activities. Children exhibited more appropriate sharing when the mother was free to interact with them than when she was busy with paperwork. The third part of the study examined the effects of two formats of a parent-training programme on sibling sharing. Families were randomly assigned to one of three conditions: individual programme, group programme, or waiting-list control. The programme provided parents with information about the development of sharing and sibling relationships and taught behavioral parenting techniques to use in promoting the development of child sharing skills. Positive effects of the sharing programme on siblings' sharing-related behavior were clearly demonstrated. These effects were seen to generalize across informants and across behaviors, but not across informants and behaviors combined. Treatment effects were maintained over a follow-up period. Although mothers demonstrated increased knowledge of the content covered by the programme and rated it highly, they did not demonstrate or report significant changes in their own parenting approach on the original measures. Mixed results were obtained concerning the two treatment formats. For observations of child behavior, only the individual format showed superiority over the control condition. The two formats did not differ in treatment effects found on most questionnaire measures. Mothers' reports of decreased behavior problems among younger children and a few tentative findings from child interview measures suggested superiority of the group format. Overall, this study demonstrated both strong relationships between the sharing-related behavior of children, and correlational and causal relationships between mother behavior and sibling sharing. A parent-training intervention was demonstrated to have positive effects on children's sharing behaviors, and these effects generalized over situations, behaviors and time. / Arts, Faculty of / Psychology, Department of / Graduate