Since its inclusion in the Hong Kong school curriculum in 2003, Cantonese opera has remained underrepresented in music education, mainly due to insufficient teacher training. This study evaluates the effectiveness of an in-service professional development programme to equip music educators with the skills and knowledge necessary to teach Cantonese opera. Four music teachers participated in a 120-hour training programme encompassing operatic singing and accompaniment, musical structures, and the historical and cultural contexts of the genre. Post-training, participants were interviewed, and their classroom practices were observed. The findings reveal that the programme significantly increased teacher and student motivation toward Cantonese opera. However, challenges persisted, including addressing colleagues' expectations, school leadership, education authorities, and student preferences. Notably, the dominance of Western classical music education emerged as a key barrier to the effective integration of Cantonese opera into school music programmes. This study underscores the importance of targeted teacher training and recommends advancing Cantonese opera education in Hong Kong. These include pedagogical innovations, curriculum reform, enhanced professional development, and supportive policy measures.