[a] Note that this measure—sometimes referred to as the “status” dropout rate—represents only one of several ways for calculating high school dropout. The “event” dropout rate reports the percentage of young people ages 15 through 24 who dropped out of grades 10 through 12 in the past year. The “cohort” dropout rate measures the percentage of an entering ninth-grade class that drops out before the end of the twelfth-grade year. The “status” dropout rate is the only measure for which there are reliable national data over a number of years. National data on cohort graduation rates show that 81 percent of the public high school class of 2012-13 graduated four years after entering ninth grade.