School connectedness (i.e., the extent to which students feel accepted, valued, respected and included in the school) has recently surfaced as one of the most important predictors of adolescent mental health (particularly depressive symptoms). Thus it is now vital to understand predictors of school connectedness. The school environment is an established predictor, but we set out to examine whether parental attachment predicts both the perception of the school environment and school connectedness and whether the perception of school environment mediates the relation between parent attachment and school connectedness. A study of 171 high school students from years 8 to 12 showed that parent attachment strongly predicted both the experience of the school environment and school connectedness. We also confirmed the mediation hypothesis that suggests that the relationship between parent attachment and school connectedness is not a direct one but largely carried through individual differences in the perception of the school environment that is influenced by parent attachment. This finding has important clinical implications in terms of shedding some insight on how multiple systems might be interlinked in influencing wellbeing in adolescents and confirms the importance of intervening at the double platform of both the family and the school system.