Once when I was teaching the difference between fact and opinion, a student said, "My brother is mean." I tried to explain that what the student said was an opinion, and she started backing up her statement with evidence. Collecting evidence to support an opinion wasn't on the lesson plan, but I went with it.
Since that day, I have made my plan more formal and created the graphic organizer shown below. To download this graphic organizer, please visit this post at Artistry of Education.