Writing is a complex skill that requires effective teaching practices in the classroom. One of the challenges English teachers in the English as a second language (L2) context face is the lack of teacher experience in teaching English writing. This brief paper reports on a small-scale study on helping Hong Kong in-service primary school teachers improve on their writing instruction through a school-based professional development programme in Hong Kong. From September to December 2013, the author taught a general English teaching methodology course of 50 h to a group of 18 in-service teachers from 15 primary schools in Hong Kong, who were undertaking the Postgraduate Diploma in Education Programme in the university. Four participants were involved in this study on a voluntary basis. The teachers reported that they became more confident in teaching how to write as a result of the school-based professional development programme. They felt that other colleagues could work well as their "mirrors" to see each other's problems in teaching as they were familiar with their students and each other's situations.