I love the book "A Bad Case of the Tattle Tongue" by Julia Cook. It's fun and interesting and includes some concrete rules for knowing when to warn an adult and when to "mind your own beeswax."
I usually begin by watching this youtube video to introduce the concept and get the kids' attention.
We then read the book and play the game "Pin the Tongue on the Tattler." The kids love it! It works just like Pin the Tail on the Donkey except you have to decide if an example is tattling or warning. You then choose the spotted tongue or the red tongue, close your eyes and try to place the tongue. The kids think it's hilarious when the tongue ends up on the forehead or way over on the board. I like that it's a lot of practice about some tricky situations of tattling or warning.
Right now the Pin the Tongue on the Tattler game is FREE on my teacher pay teachers store!!! Check it out! And while you're at it, like us on Facebook!
Update: The time has passed to get the Tattler game for free. Check out my store for other great, free products or purchase the game for $4.