An analysis of projection errors from the past 22 editions of Projections of Education Statistics indicates that the mean absolute percentage errors (MAPEs) for lead times of 1, 2, 5, and 10 years out for projections of public school enrollment in grades PK–12 were 0.3, 0.6, 1.2, and 2.4 percent, respectively. For the 1-year-out prediction, this means that one would expect the projection to be within 0.3 percent of the actual value, on average. For projections of public school enrollment in grades PK–8, the MAPEs for lead times of 1, 2, 5, and 10 years out were 0.4, 0.6, 1.3, and 3.3 percent, respectively, while the MAPEs for projections of public school enrollment in grades 9–12 were 0.4, 0.7, 1.3, and 2.3 percent, respectively, for the same lead times.
Projections of public elementary and secondary enrollment produced by the National Center for Education Statistics (NCES) over the last 23 years have been more accurate than projections of public high school graduates produced by NCES over the same period. For more information, see table A-2 in appendix A.