I've mentioned it before but it came to mind again after reading a response to august06mom's post below. I get kind of exhausted reading about all the lights and what they mean and how they relate to behavior, I can imagine a 5 year old child new to the school setting might be a little overwhelmed by it.
DD's school doesn't do anything like this, so admittedly I don't have any direct experience with it, but it kind of feels like it is a little overdone at this point? I don't remember having this when I was in (public) school as a child either.
Re: Red lights, green lights, orange lights, yellow lights...
Both of my K kids only have green, yellow, and red lights. They were in a daycare center prior to K so it's pretty clear to them how it works.
We didn't have lights per se, but instead you'd get your name written on the board. If it continued, you'd get a check mark by your name.