Evidence collected through comparison of compensatory education students' calendar year and school year gains implies that summer drop-off of basic skills is a common phenomenon. There are two possible interpretations of this finding. The first, "forgetting," assumes compensatory education students know less in the fall than they did the previous spring. The "no growth in summer" interpretation assumes that the students do know as much in the fall as in the previous spring. The results of the National Institute of Education's Instructional Dimensions Study provide strong evidence in favor of the "no growth in summer" model. Students whose initial test scores were at or above the national norms make substantial gains during the summer, but compensatory education students do not. Compensatory education programs are therefore doing some good and should be continued until effective alternatives can be found. Summer school programs might foster achievement gains during the summer months, but they do not attract many disadvantaged students and their programming is not focused on basic skills instruction. Public programs may be unable to overcome the problem of summer drop-off entirely. Further research into the summer drop-off phenomenon is needed to understand the limits of public policy and maximize the effectiveness of compensatory education programs. (Author/MK)