The gruesome task of being a substitute isn't made easier by not knowing the names of students. So, I prepare strips of paper to lightly tape beside the list of name in the roll. When each student replies, the sub can make a quick not of the most obvious feature of the student (glasses, red hair, torn jeans). Then if Mr. Red Hair needs attention, a subtle look at the notes makes it easier to come up with a name. Saying the student's name will get some respect real fast!