My students work in groups of four and during test times there is quite a temptation for eyes to wander. I make my students responsible for keeping their papers covered. Whenever I see answers uncovered, I quietly place a small red square of construction paper on the student's desk. This is a warning and a reminder. If a second red square is placed on the same student's desk during the same test, one point is deducted. Each time thereafter, another point is deducted. I never have had to deduct more than one point and I no longer have to nag the class to keep their answers covered.