Let's begin with some Mental Math...
Talk to your partner about which one you think your students would pick? Why?
What is your proof?
How are you reasoning and applying your mathematical understanding?
Convince others!
What does this sharing sound like?
The "Which One Doesn't Belong" website has several examples of open ended thinking tasks. It is an open source site, so you will want to work through the problems yourself prior to using them with your students in order to allow you to determine a reason why each square does not belong- it also is a good way to anticipate your students' answers.
Accountable Talk: Support one another in your thinking and in anticipating student responses using the Math Prompts that Cathy Marks Krpan shares in her book Teaching Math with Meaning.
Are you thinking about effective questions that you can ask your students in order to provoke thinking and deepen conceptual understanding in math? Browse through "Asking Effective Questions."
For more about promoting accountable math talk in your classroom, take some time later today to work through the module "5 Practices for Productive Talk in Math Class."