In the implementation of a 10-year educational reform since the turn of the century in Hong Kong, assessment has been one of the key areas of change. The importance of changing assessment practices in the process of teaching and learning has been discussed in various government documents since 1990. In the past, assessment practices were inclined to be mainly "assessment of learning" which was more summative in nature. In the reform, schools were encouraged to put more emphasis on "assessment for learning" which was considered more of a formative nature. On approaching the mid point of such reform, significant difference in its degree and scope of development can be seen in schools. In this particular paper, the focus is assessment reform in the primary school sector. The two concepts in assessment are explored by a detailed documentary analysis of assessment policies written on basic education over the last decade. Together with reviewing the current developments on assessment change in primary schools, implications for more effective use of assessment for enhancing teaching and learning are made.