There has been much debate over the role of grammar instruction in the teaching of writing -- whether grammar and writing should be taught separately, or in an integrated manner in the English Language writing class. This paper describes an action research project aimed at contributing to this debate through some teachers' reflections on integrating grammar and writing in the writing class. Five experienced English Language teachers in a Singapore primary school were concerned that while their students performed reasonably well in grammar tasks done in isolation, they struggled with the effective use of grammar in writing tasks. The teachers participated in the project by attending professional development sessions to enhance their knowledge of grammar as a meaning-making resource, before engaging in teacher inquiry of some student compositions to better understand how their students used grammar in writing. They then proceeded to revise existing writing instructional materials to explicitly integrate grammar and writing. Finally, the teachers were asked to reflect, on paper, on their experience in being part of the project. Results show that the action research process led to teachers' enhanced grammar content knowledge, better understanding of students' gaps in writing, and improved teaching practices in the writing class.