Recent research has begun to acknowledge that parents of school-aged children with intellectual and developmental disabilities experience both positive and negative impacts when raising their children. Since some parents report feelings of a positive and a negative nature concurrently, within families research must attempt to discover the psychological variables that foster adaptation. This thesis aimed to extend current research in three ways. First parental cognitive variables and their incorporation into existing models of adaptation were critically discussed (Chapter 2). Second, relatively unstudied psychological variables were investigated with respect to both positive and negative parental adjustment. Third, longitudinal methodologies were used to draw conclusions as to the causal directions of the relationships and to ascertain whether the psychological variables acted as moderators or mediators i. e. were state- or trait-like. In Study I (Chapter 3) acceptancew as a psychological variable that was found to be associated with maternal well-being. Mothers who were generally more accepting reported fewer psychological adjustment problems. Acceptance entered into a bi-directional relationship with anxiety and depression. No significant associations were found for mindfulness and maternal well-being. Parental locus of control was examinedi n Study 2 (Chapter 4) and was significantly associatedw ith measures of both maternal positive perceptions and with maternal distress. Furthermore, dimensions of parental locus of control were significant predictors of negative maternal adjustment. Parental internal-external locus of control was related bi-directionally to stress over 18 months. Hope was the focus of Study 3 (Chapter 4) and was analysed separately for fathers and mothers. For mothers, hope was predictive of depression and positive affect and child behaviour problems predicted maternal depression. For fathers, hope was predictive of anxiety, depression and positive affect. An interaction effect was found for hope agency and pathways in the prediction of maternal depression such that mothers reporting high levels of both hope dimensions reported the lowest levels of depressive symptoms. Findings from the three empirical studies were discussed in relation to their theoretical value and their implication in intervention research. Recommendationsfo r further study were made, which included a call for further stringently defined study into an area that has the potential to be a valuable assessment tool for intervention work.