Much of the research that has examined the writing knowledge of school-age students has relied on interviews to ascertain this information, which is problematic because interviews may underestimate breadth and depth of writing knowledge, require lengthy interactions with participants, and do not permit a direct evaluation of a prescribed array of constituent knowledge elements. For these reasons, our goal in this study is to report the development, piloting, and field testing, using a sample of 335 students from grades 4 and 5, of four alternate versions of a writing knowledge assessment—the Student Knowledge of Writing Test (SKOWT)—that uses forced-choice responses to evaluate students’ knowledge of writing processes, genre elements, and linguistic features of written language. All versions of the SKOWT demonstrated adequate internal consistency reliability and construct validity based on exploratory factor analyses following deletion of some items. In addition, there was acceptable predictive criterion validity based on associations of SKOWT scores with subtests from the Test of Written Language-4 and measures of narrative, opinion, and informative essay quality. We discuss how the SKOWT might be used in future research and educational practice.