This paper reports on an analysis of large-scale assessments of Grades 5-8 students' writing across 10 provinces and 2 territories in Canada. Theory, classroom practice, and the contributions and constraints of large-scale writing assessment are brought together with a focus on Grades 5-8 writing in order to provide both a broad view of Canada-wide assessments and specific recommendations for enhancing the validity of provincial and territorial writing assessment in Canada. We deductively analyzed the primary assessment administration documents found on the provincial and territorial education websites using the categories of (a) design (e.g., grades at which the tests are written, the goals of the tests, the number and types of written compositions that are gathered, (b) administration (e.g., time of year, length of time provided to students to write, and pre-writing activities), and (c) the scoring of the assessments. We also used tenets of effective writing assessment from a process writing approach and from a multiliteracies approach to analyze the assessment procedures. Our analysis shows that process writing approaches have influenced the administration procedures in terms of the provision of time to talk with peers before writing and the recognition of various composition and thinking processes. However, composing processes are directed to be less idiosyncratic and recursive than composition theorists and noted teachers of writing would recommend. The assessments do not yet reflect an awareness of multiliteracies theory, as there is little use of digital technology to write and portfolio assessments and the collaborative writing of Web 2.0 practices are non-existent.