Iowa had the highest four-year high school graduation rate in 2010-11, the U.S. Department of Education disclosed as it released for the first time data in which states used a common measure.

The department says the greater uniformity of the data will enable educators to provide more meaningful comparisons of graduation rates in states and school districts. Previous methods used by states varied and made comparisons between states unreliable.

"By using this new measure, states will be more honest in holding schools accountable and ensuring that students succeed," U.S. Secretary of Education Arne Duncan says in a news release. "Ultimately, these data will help states target support to ensure more students graduate on time, college and career ready."

The department notes that the graduation rates compiled in the new system cannot be compared with the rates reported by states in past years, so increases or decreases in the 2011-12 percentages should not viewed as improvements or declines, but as "a more accurate snapshot."

The rates listed by the education department are four-year adjusted cohort graduation rates. The department defines that rate as “the number of students who graduate in four years with a regular high school diploma divided by the number of students who form the adjusted cohort for the graduating class.” Students that are entering ninth grade for the first time form a cohort, which is adjusted over the next four years by adding any students who transfer in and subtracting those who transfer out, emigrate to another country, or die.

The rates for 2010-11 range from 88 percent in Iowa to 59 percent in Washington, D.C. Rates for three states—Idaho, Kentucky and Oklahoma—were not included in the education department data.

The rates also are broken down by racial and ethnic groups. Graduation rates for black or African-American students was highest in Texas and Montana (81 percent), and lowest in Nevada (43 percent). For Hispanic/Latino students, the highest graduation rate was in Maine (87 percent), and the lowest rate was in Minnesota (51 percent). For Asian/Pacific Islander students, the highest graduation rate was in Texas (95 percent), and the lowest rate was in Minnesota (72 percent). For white or Caucasian students, the highest graduation rate was in Texas (92 percent), and the lowest rate was in Oregon (70 percent).

--by Mike Kennedy


MORE: View the state rankings of 2010-11 four-year high school graduation rates.