In education research, a "sleeper effect" is not a way to get all of your preschoolers to take naps. Instead, it is an outcome of a program that appears not immediately after the end of the program, but some time afterwards, usually a year or more. For example, the mother of all sleeper effects was the Perry Preschool study, which found positive outcomes at the end of preschool but no differences throughout elementary school. Then positive follow-up outcomes began to show up on a variety of important measures in high school and beyond.