Adopting a lifespan developmental perspective, this study views adolescent mental health as the result of dynamic interactions between past and present experiences. The study aims to investigate two potential pathways through which stressful events experienced earlier in life may influence an adolescent's current mental health: These pathways are : (1) the long-term direct effects and (2) the short-term indirect effects mediated by current stress. A longitudinal study tracked 9642 fifth graders (51.5% male; mean age = 10.37±1.38) over five years, conducting annual assessments. Self-report data were collected on stressful life events, as well as on symptoms of depression and anxiety. Regression and mediation analyses were conducted. Analyses controlling for gender, age, SES, and T1 mental health problems showed the following: (1) T1 stress significantly and positively predicted T5 mental health problems (β_depression = 0.690, p < 0.001; β_anxiety = 0.417, p < 0.001); and (2) complete mediation emerged for depression, with T1 stress exerting a significant positive indirect effect via T5 stress (β = 0.686, p < 0.001) , but no significant direct effect on T5 depressive symptoms (β = 0.001, p = 0.941). (3) For anxiety, competitive mediation emerged, with T1 stress exerting a positive indirect effect via T5 stress (β = 0.602, p < 0.001) as well as a significant negative direct effect on T5 anxiety symptoms(β = -0.186, p < 0.001). The findings suggest that the detrimental effects of stress experienced earlier in life on the mental health of adolescents are largely explained by current stress. Therefore, interventions targeting the reduction of current stress may promote positive mental health outcomes.