We read a social story I found on Teachers Pay Teachers. Just in case you haven't heard of them, social stories are a story (sometimes written and sometimes totally visual) originally used for students with autism to describe a social situation. They usually explain the situation or concept and help the students understand the accepted behaviors in this situation. They also usually explain the ways others may behave in the situation. Even though they were originally for use with special ed, I noticed some counselors talking about them on blogs so I thought I'd try it. I love social stories and Teachers Pay Teachers probably has one for almost every situation, some of which are free.
After we read the story and practiced using "I messages" (which are part of the story), we did a cut-and-paste activity (available here for free) in which the students sort different situations into tattling or reporting.
The social story is by One Giggle At A Time (Click here to go to her store)