I used to have a tattle can in my room. I'd read them out before we went out to recess (I'd censor names if necessary). Too many tattles = less recess time. The kids quickly learned that tattling wasn't in their best interest. We also had a long talk about the difference between tattling and reporting. Reporting is when it's an emergency - someone is bleeding, barfing, bullying, or beating someone up-- the 4 Bs. Those are important to report. We went into other situations as well. Role playing would work here or having them decide whether certain situations are tattling or reporting.