One of the changes in the common core standards is going from persuasive writing to argument writing. It is more difficult to write and also to teach. These skills may be the most important ones teachers pass on to their students. That is why I am reading: Teaching Argument Writing by George Hillocks, Jr.
The book is advertised for grades 6-12, but I feel 4th and 5th grade teachers would gain from it, too. I've only begun reading, but already in the first three chapters it teaches simple arguments showing step-by-step how to teach students how to write and evaluate.
Anything that helps teachers teach students to problem solve, write arguments and support their claims---it gets my attention!