Your characterization of the Education Week methodology (see here) as analyzing "the percentage of 9th graders who completed high school four years later" isn't quite correct. The formula on page 12 of the Ed Week report does, indeed, make use of dropout rates from grade to grade, but all dropouts are calculated between the same pair of years. EdWeek describes this as likelihood of graduation "given the schooling conditions prevailing during a particular school year." So it is a kind of synthetic estimate of dropouts for a cohort of ninth graders.
I'm writing this because some of the dropout methodologies do try to track a cohort of ninth graders over four years, but Ed Week adds a twist to that approach. Also, since this is a topic you cover from time to time, I thought the difference should be brought to your attention.
Emerson J. Elliott
National Council for Accreditation of Teacher Education
