You might be wondering what they have to do with persuasive writing. OREO is a mnemonic device. It helps the students remember the format for persuasive writing. O stands for opinion. R is for reason. E is for explanation and the final O stands for opinion again.
When I introduce persuasive writing I show kids the pack of cookies and I give them two white circles stapled between 2 black circles. They decorate the front as an Oreo and then we go through each letter. The kids write the words opinion, reason, explanation, and opinion inside as we orally give examples. I model persuading the kids that Oreos are delicious and then I go around the room and ask them to give me their opinion about Oreos. They also must give me a reason and explanation. Once each student tells me what he or she thinks we all eat Oreos together.