Our new unit is Opinion writing and in particular, "Writing Reviews". Students were invited to bring in a favorite personal collection of theirs and judge how they would rate them: 1st, 2nd, 3rd, etc. They spent time judging all they have collected, thinking, "This is the best because..." They are trying to convince others of their opinions.
A few days later, students visited tables with other children's collections and rated what they thought was the best and why. It was a time when they learned that writers don't always share the same opinion. When people disagree, this leads writers to back up their opinion with reasons.