"The ability to write logical arguments based on substantive claims, sound reasoning and relevant evidence is a cornerstone of the writing standards, with opinion writing - a basic form of argument - extending down into the earliest grades." (Source: Key Points in English Language Arts Common Core State Standards) Here are some resources to help your students improve their argumentative writing skills.
The Special Place of Argument (pdf)
Student Writing Samples
Argument, Persuasion, or Propaganda? (pdf)
Introductions, Body Paragraphs, and Conclusions for an Argument Paper
Logic in Argumentative Writing
Teaching Argument Writing, Grades 6-12 (Book)
Inquire: A Guide to 21st Century Learning
The Toulmin Model of Argumentation
The 7 C's of Argumentation
Video: Socratic Seminar: Supporting Claims and Counterclaims
What is an Argumentative Essay?
Argumentative Writing Rubric (pdf)
Writing an Argumentative Essay
Persuasive / Opinion Writing Resources
Analyzing Famous Speeches as Arguments
Argument, Persuasion, or Propaganda? Analyzing World War II Posters
Finding Common Ground: Hypothetical Scenario (pdf)
Finding Common Ground
For and Against graphic organizer
Interactive Venn Diagram
Pioneer Library SIRS Knowledge Source: Leading Issues (pdf)
The Six Traits of Effective Writing Tutorial
So You Think You Can Argue
Videos: How to Write an Argument Essay