Articles
See what Marilyn Burns has to say about writing in math in Math Journals Boost Real Learning (see below).
Talking, Writing, and Reasoning: Making Thinking Visible with Math Journals (Lesson plan with helpful resources)
http://www.readwritethink.org/classroom-resources/lesson-plans/talking-writing-reasoning-making-820.html
Models/Examples
Adventures in Guided Math - Math Journals
http://www.guided-math-adventures.com/?p=102
Tunstall's teaching Tidbits - Using Interactive Notebooks With Young Learners
http://tunstalltimes.blogspot.com/2014/09/interactive-notebooks-and-young-learners.html
Tunstall's Teaching Tidbits - About Math Journals
http://tunstalltimes.blogspot.com/2014/12/about-math-journals.html
I'm Lovin Lit - Interactive Notebooks FAQ (While this relates to ELA notebooks, the general tips are very helpful.)
http://imlovinlit.com/2014/07/21/interactive-notebooks-faq/
The Cornerstone - Everything You Need to Know About Math Journals
http://thecornerstoneforteachers.com/free-resources/math/math-journals
Prompts/Ideas
Show What You Know - Grade 1
http://web.archive.org/web/20060615113019/http://elementarypgms.brevard.k12.fl.us/Show1.pdf
Show What You Know - Grade 2
http://web.archive.org/web/20060615113032/http://elementarypgms.brevard.k12.fl.us/Show2.pdf