This paper aims to explore the shared features of effective professional development programmes for improving teachers' assessment literacy (AL). On the basis of the literature review of 17 empirical studies related to teachers' AL improvement, the features of effectiveness can be categorized into three themes: 1) What (Content): The programme content should be contextualized and tailored to the teacher's assessment training needs; 2) How (Method): The delivery method should help to build a collaborative learning community, advocate active engagement, and provide continuing professional development opportunity; and 3) Why (Orientation): The programme should be oriented to cultivate teachers as reflective practitioners and to facilitate their identity (re)construction as assessors. The implications for future research are also discussed to direct further efforts in teachers' AL improvement.