You might remember that I was missing one of my students, but she turned out to be with her dad because she doesn't go to the after school program on Wednesdays. Well, her teacher uses an extremely simple technique which helps him keep track of where students are or are going.
At the end of every class, he has every one of his kindergartners look him in the eye and then, say "bye." On the surface, it looks like all that's being done is saying good bye, but there's a little more to it than that. You don't want your kindergartners leaving if they don't have a trusted adult to go with. So, if a kindergartner says "bye" to you, you figure that it's because a trusted adult is in proximity. But, if you look at the kindergartner straight in the eyes, you look up, and see no trusted adult, then you know that that kindergartner should not leave.
Also, because you establish the routine that students must look you in the eye before they leave, you're reassuring yourself that your kindergartners aren't just walking off. In that case, you wouldn't know what to think about their whereabouts. Whereas, if they look at you in the eyes while saying good bye and you immediately see a trusted adult within range, you know that each and every individual kindergartner is accounted for. That's the significance of an eye to eye farewell for each and every individual kindergartner.