Adolescent mental health in Nigerian urban slums is a growing concern due to socio-economic challenges and limited access to healthcare. Participants were recruited from three randomly selected schools in urban slums. Screening included self-report questionnaires and interviews. Six-month assessments measured changes in mental health indicators. A notable trend was a significant increase (p < .05) in reported depressive symptoms among participants who received the screening compared to controls, highlighting the need for further intervention development. School-based mental health screenings showed promise but require tailored interventions and support mechanisms to achieve sustainable improvements in adolescent well-being. Develop targeted educational programmes aligned with screening outcomes and advocate for policy changes to improve access to mental healthcare services within urban slums.