Adolescent girls in southern Nigeria face significant nutritional deficiencies that impact their growth and mental health. A mixed-methods approach will be employed, including baseline surveys, quarterly dietary assessments using a validated food frequency questionnaire (FFQ), and follow-up assessments to measure impact over six months. Psychosocial data will be collected through semi-structured interviews with students and teachers, supplemented by qualitative thematic analysis. Dietary improvements were observed in approximately 75% of participants, leading to a significant increase in hemoglobin levels (mean increase: 10g/L) within the first three months. Qualitative data suggest improved self-esteem and social interactions among students involved in intervention programmes. School-based nutrition interventions appear effective in enhancing adolescent girls' nutritional status and mental health, warranting further implementation and evaluation. Interventions should be tailored to local contexts and evaluated regularly to ensure sustained benefits. Training for educators on nutrition education is recommended to support intervention delivery. Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.