ASCD has made this chapter of Laney Sammons' book available openly online. In particular, beginning at Figure 5.3 (Teaching Point Suggestions for Mathematical Writing) several tables and other suggestions are especially helpful.
RAFT assignments encourage students to uncover their own voices and formats for presenting their ideas about content information they are studying. Students learn to respond to writing prompts that require them to think about various perspectives: Role of the Writer, Audience, Format, and Topic.
While the examples in this Teaching Children Mathematics article are designed for elementary school mathematics, the strategies and support carry through to grades 6-12.
Although this article is from an elementary-grades journal, the strategies and tools illustrated fit well in secondary classrooms as well. “Moving Math in the Write Direction” by Shannon Bostiga, Michelle Cantin, Cristina Fontana, and Tutita Casa in Teaching Children Mathematics was also featured in The Marshall Memo, May 10, 2016. You must have an NCTM membership to view this article.
Purdue University's Online Writing Lab has a number of resources, including this brief summary of Toulmin's approach to argument. The terminology here should be familiar to students from their ELA coursework (and ideally, science and social studies, too).
This article by Dr. Kevin Lee from UC-Davis is very accessible at the high school level and informative for 6-12 teachers. Lee's conversational tone helps students learn how to formally present their ideas.
This free course from the Annenberg Learner "What is Disciplinary Literacy?" provides depth and background for mathematics teachers.
While the examples in this blog article are from the college level, the strategies are applicable and translatable to the middle school and high school level.
This ASCD Educational Leadership article highlights various types of writing (with elementary grade examples) as a way to deepen learning.
This resource provides supplementary Algebra 1 assignments that require students to analyze correct and incorrect examples. It targets common misconceptions and errors, providing practice with mathematical argumentation.