A friend of mine from New Orleans recently posted this photo from school of his nephew showing a cell-phone-holder-board to keep track of who is present in class.   This is an excellent example of a simple LEAN TOOL.  It results in MISTAKE PROOFING ( Poka Yoke ) the process of keeping track of who is actually present in the class, and at the same time is an excellent example of VISUAL MANAGMENT.   #LeanSchools  The best lean tools are often the simplest !