School connectedness has been shown to support adolescents' academic adjustment by fostering academic performance. However, the specific association between school connectedness and attentional difficulties in class has not been previously examined, nor have the potential mediating factors underlying the broader relationship between school connectedness and academic adjustment. Positive Youth Development (PYD) has also been identified as a predictor of academic adjustment in youth. This study aimed to examine the mediating role of PYD in the relationship between school connectedness and two indicators of academic adjustment, perceived academic performance and difficulty paying attention, in a sample of Spanish students enrolled in compulsory secondary education (n = 1,036; 50.3% boys; Mage = 14.17; SDage = 1.34). A cross-sectional study was carried out using an anonymous questionnaire. School connectedness was associated with higher perceived academic performance and fewer difficulties paying attention in class. Three dimensions of PYD (i.e., character, confidence and competence, but not connection and caring) partially accounted for the relationship between school connectedness and the indicators of academic adjustment. These findings have implications for interventions aimed at enhancing students' academic adjustment, highlighting the importance of integrating the promotion of PYD and school connectedness to achieve more effective outcomes.