In the Netherlands, nationwide assessments are periodically executed to evaluate the quality of teachers' writing instruction and students' writing in primary schools. These assessments provide an empirical basis for the societal debate about the content and level of writing education, and enable the Inspectorate of Education to monitor the quality of teaching practices However, educational quality is a complex, multidimensional construct. In this literature review we discuss the question which domain-specific and more general teaching variables at the classroom level could be incorporated in nationwide assessment instruments, such as teacher questionnaires and classroom observation instruments. Based on theoretical and empirical studies on writing education, we propose a framework of variables which appear to be relevant, in the sense that they have been found to be characteristic of high-quality writing instruction. This framework can be used for the development of assessment instruments, and can also be a valuable resource for writing researchers, curriculum designers, and teachers.