Anxiety disorders are prevalent among high school students in Nairobi, Kenya, with significant negative impacts on academic performance and mental health. A mixed methods design was employed, incorporating both quantitative survey data collection and qualitative semi-structured interviews to comprehensively assess programme impact. The survey revealed a statistically significant reduction (p < 0.05) in overall anxiety levels among participants following the intervention compared to pre-intervention scores. School-based mental health programmes show promise in mitigating anxiety disorders among high school students in Nairobi, with substantial improvements reported post-programme implementation. Further research should explore long-term effects and scalability of these interventions across different socio-economic backgrounds.