I have "Mystery Worker" reward cards always on hand to use and as needed I say, "I'm watching a Mystery Worker". That phrase works like MAGIC. Students quiet down and get to the task at hand. Then for a brief amount of time, usually for 10-15 minutes, I observe my target student. At the end of my "sleuthing" I decide whether the student earned the "Mystery Worker" honor. If they did, I hand them the card with a note explaining how they set a good example. If by chance the honor was not earned, I never reveal who I was watching. I do keep a running checklist of who I've targeted, so I can be sure to try and honor every student at some point. Many of us have probably used the "Mystery Walker" in a similar way to target line behavior or transition times. I just took the idea a step further and brought it into my regular classroom teaching routines. Give it a go and see if it cracks the case of the craziness that can hit your classroom sometimes.
Don't let it be a MYSTERY if you are a follower of my blog.