I created these for my intermediate students and they really bought into it. I started off writing them myself, but as time passed we took the time to learn how to write sincere, detailed praise and thanks and it took off from there. Looks great on coloured paper and taped to the entrance of the classroom door. At the end of the year, pile up each student's 'shout-outs' and present them. I have pinned a couple other templates - for variety on the wall.
While students are working problems, walk around the room with a handful of green pens. When someone finishes the problems correctly, they get a green star and a green pen. Now they are qualified to coach and star papers for other students, and so on, until everyone is done.