Previous studies highlighted the importance of parental support for development of mastery of control and depressive symptoms. These studies tended to examine one time wave and outcomes related to that period, forwarding an assumption parenting behaviours do not change as children age. Using the National Longitudinal Survey of Youth 1979-Children and Young Adults, this study filled the gap by examining children's supportive environment at three time points and determining how levels of support across these points impacted children's depression and mastery at 18 years of age. Relative stability of mothers' supportive parenting (i.e., encouragement of social maturity, warmth and affection, and physical punishment) at early childhood, middle childhood, and early adolescence was examined by Kendall's tau correlations. Encouragement of social maturity showed relative stability between early and middle childhood and middle childhood and early adolescence; warmth and affection showed relative stability between early and middle childhood, and physical punishment showed relative stability across all time points. Absolute stability was examined using hierarchical linear modelling and Wilcoxon signed-rank test. No instances were found. Latent class growth analysis identified different trajectories of supportive environment among participants and three groups were identified. Multiple regressions conducted to examine how different trajectories affect late adolescents' depression and mastery found children of mothers from the least supportive group had statistically significant higher level of depression and lower level of mastery of control at 18 years of age; children of mothers from the progressively and continuously supportive group had similarly positive results of depression and mastery.