A review of relevant literature indicates that assessment of students’ academic writing needs to include formative as well as summative feedback, especially when process approaches to the teaching of writing are adopted. However, in Malaysia, assessment is perceived as mainly for grading purposes and the teaching and learning of academic writing are firmly based on a product approach. The present study took the form of a collaborative action research project intended to consider the extent to which elements of process writing and formative assessment could be introduced, from a sociocultural perspective, into the normal classrooms of two Malaysian ESL teachers and 48 learners at a selected Malaysian university. This project was carried out in three phases. Phase 1 gathered documentary and interview data on current issues pertaining to ESL writing assessment practices in Malaysian tertiary classrooms. Phase 2 was carried out through two action research cycles during which a formative assessment intervention was introduced in classroom teaching. Interviews in Phase 3 were conducted to discover the immediate and long-term impacts of this action research project on teachers’ beliefs and subsequent pedagogical and learning development. The data from documents, interviews, classroom observations, briefing and feedback sessions were subjected to a process of grounded analysis. From the analysis, categories and themes were generated and structured to address to the research questions formulated for this research. The present study suggests that process writing is more meaningful to the learners when formative assessment is incorporated into the teaching of ESL writing. It allows more opportunities for ESL learners to gain feedback and feed forward from both teachers and peers. Through feedback and feed forward, learners were given an opportunity to develop their understanding based not only on their previous mistakes but also on the new input to improve their writing. In addition, the use of feedback and feed forward helped both teachers and learners learn to view assessment in a positive way. However, it was evident that any intention to integrate curricular innovations, such as formative assessment and process writing, must acknowledge the institutional and sociocultural contexts of the participants, and thus be tailored to fit in with normal pedagogical activity. The findings of this study were viewed through the lens of sociocultural theory. By interpreting the implications of the study in terms of mediation, scaffolding and regulation, the basic construct of a Zone of Proximal Development (ZPD) was refined to formulate a specific zone of writing development (zwd). This is intended to shed light on the actual means by which learners can be enabled to perform written tasks with structured guidance so that they can eventually do similar tasks without assistance. The overall results of this study contribute to the contemporary debates in Malaysia about alternatives to current assessment practice. Closing the gap between teaching and assessment, through the integration of formative assessment and process writing, within a basically product approach, is intended to be the main contribution of this research. The study makes a contribution to the areas of both writing instruction and writing research. Blending the existing practices with elements of process writing and formative assessment highlights the usefulness of peer review activity within a ZPD through the practice of scaffolding. Also, this study adds to the importance of doing action research collaboratively and in a collegial manner, with a longitudinal perspective. Although the setting of the research was in Malaysia, the findings of the study could provide guidelines for research elsewhere, the collaborative approach to action research applied in other contexts, and appropriate modification of the ZPD (in this case, a zwd) could be applied to enhance the teaching of other skills.