Second language (L2) writing research embraces a plurality of epistemological stances, theories, and occasionally, competing paradigms. Some researchers ask whether it is possible, or even desirable, to develop a comprehensive theory of second language writing. This is an important question in view of the fact that students learn their L2 under different circumstances within any given country and across the world. Because theories guide both research and practice, the authors set out to examine a theoretical framing in L2 writing research in pre-kindergarten through high school (P-12). Recognizing the significance of the theory/practice relationship for researchers and educators, this analysis articulates the major theoretical strands in L2 writing over the past 20 years (1990-2010), with an explicit focus on research in writing instruction P-12. The authors' main guiding question was: What is the nature of theorizing in L2 writing instruction P-12? They also developed several subquestions related to this main question, which they explore later in the text. They first present the method and findings, followed by implications for research and practice. They also offer some suggestions on how to move the field of L2 writing instruction forward. (Contains 5 tables.)