Before a student can tattle on another student, she or he must give two compliments about that student. This sets the tone for positive talk at behavior checks, and really helps keep the students thinking positively about their behavior. Positive statements should be as specific as possible. Negative statements should be as nonjudgemental and free from emotion as possible. Have someone keep a tally of your statements for a half-hour or so.
Some teachers wear a counter on their risk to keep track of their statements.
Try going an hour with no negative statements. Gradually increase the time between behavior checks. This is part of extinction. I usually increase the interval from a half hour to an hour after a few months. At the hourly behavior checks, the students discuss and give themselves marks for behavior in the two preceding time slots.