The newest problem with graduation rates

The Washington Post reports:

School administrators across the country have been expressing their concern over the federal government’s changes in reporting graduation rates. Starting with the 2010-2011 school year, all high schools have been required to provide data based on the four-year “cohort” rate. In some states this method has already resulted in graduation rates as much as 20% below those formerly reported.

That should not surprise those who availed themselves of the summary data on schools available on the web from government sources. The data for each public school includes a breakdown of the number of students at each grade level for a given year. Thus you can see the difference between the number of students who entered the school as freshmen, and the number of seniors who were there to graduate four years later.