My kids' school uses something similar. Kids earn "gotchas" when they're 'caught' being Kind, Safe or Responsible. The focus is on reinforcing the behavior that you want to see, rather than catching kids being 'bad' and calling that out. The gotchas are put in a bin, and every couple weeks, there's a drawing for a gotcha prize (read cheap Oriental Trading toy). I could do without that aspect. The class can also earn class gotchas for good behavior walking between the classroom and PE/music/library, or for lunchtime behavior (and I think for subs sometimes).
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I will say that it works really well, and we don't have the drama associated with getting a yellow or a green. It's also based on research-based practice (PBIS) and I'm more comfortable. There are sanctions for egregious misbehavior (you get sent to the "Thinking Room" during recess and a note gets sent home). Kids who have continual problems get behavior plans and the teachers work with them to implement the behaviors they'd like to see. This is perhaps the best aspect, because it reduces the constant "you got a red today" stuff - if it's clear the child needs extra support to succeed behaviorally, they get it.