In the era of education reform in Hong Kong, in various government documents, different concepts and functions of assessment were introduced to the community (Education Commission, Sept, 2000; Curriculum Development Council, 2001). Assessment is proclaimed as an integral part of the education process. Formative assessment is stressed as a way to improve teaching and the learning of pupils. It takes place in the classrooms, and provides short term feedback to teachers so that learners' strengths and weaknesses in relation to their progression can be identified. Then teachers can use the feedback in planning what to do nest in order to enhance learning and to promote teaching effectiveness (Black, 1993). Thus, in the lessons, teachers can provide pupils with various learning activities in line with the inquiry approach, have more interaction with the pupils, and carry out different assessment tasks to evaluate individual pupils' knowledge and understanding, skills, as well as values and attitudes (Curriculum Development Council, 2002). The aim of this paper is to study the student teachers' implementation of formative assessment in local primary school classrooms. It is hoped that the present study will provide some insight for the practicing teachers when they plan to conduct formative assessment in General Studies lessons in order to enhance the learning of the pupils and promote the effectiveness of their own teaching. In response to the education reform, the researcher invited fifteen student teachers of the Postgraduate Diploma of Education (Full-time)(Primary) Programme to be co-researchers of the present study. They were to implement formative assessment in General Studies lessons during their teaching practice. They collected data and reflected on the implementation of formative assessment practice in their classroom teaching by writing weekly reflection reports, videotaping a lesson, interviewing their pupils and being interviewed by the researcher. When preparing