Graduation rates for D.C. public high schools rose slightly in 2010, but were calculated with a method that the District will scrap next year in favor of a more stringent formula likely to show a drop in completion rates.

The overall high school completion rate was 73 percent last year, up from 72.3 in the 2008-09 academic year, according to data released by the Office of the State Superintendent of Education (OSSE) Tuesday evening. Figures for public charter high schools are not yet complete, officials said.

Nationally, the overall high school graduation rate is just under 75 percent.

Graduation and dropout data can be sliced and diced in numerous ways. Under the current formula, OSSE divides the number of graduating seniors by the sum of that number plus those who have left in each of the preceding four years. But experts say the formula lacks rigor, and beginning next year the Department of Education is requiring states to calculate completion rates with the “adjusted cohort” method.

It means that the rate for the class of 2011 will be calculated by factoring in not just the students who leave, but those who enter a school at any time during the preceding four years. It is anticipated that the new formula will produce lower, but more accurate, rates. While the cohort method will be used on this year’s graduating class, the District doesn’t have to employ it to calculate rates for AYP status until 2012.

Something closer to a more accurate view of DC high school completion rates can be gleaned from a new Education Week study, which uses another method, placing the the 2008 rate at 43 percent.

In any event, rates at individual high schools under the current calculus varied widely in 2010. Two schools operated by outside partners under contract with the District did not fare especially well. Anacostia, run for the last two years by Friendship Public Charter Schools, had a graduation rate of 57.8 percent. Dunbar, managed at the time by Friends of Bedford ( before it was ousted late last year) had a rate of 68.2 percent. But Coolidge, still under Bedford’s administration, had one of the city’s highest rates in 2010 (95.3), topped only by Banneker (99.5), Ellington (96.36) and Roosevelt STAY (100)

Here’s the full list of rates with the number of seniors who graduated in 2010 in parentheses

Anacostia: 57.84 (177)

Ballou 75.69 (218)

Banneker 95.51 (85)

Cardozo 66.82 (143)

Columbia Heights 68.12 (141)

Coolidge 95.30 (142)

Dunbar 68.07 (162)

Eastern 63.67 (163)

Ellington 96.36 (106)

Luke C. Moore 61.44 (94)

McKinley 91.71 (199)

Roosevelt 55.16 (139)

School Without Walls 93.10 (108)

Spingarn 74.47 (70)

Wilson 82.46 (329)

Woodson 80.70 (138)

Roosevelt STAY 100 (77)

Spingarn STAY 86.61 (97)

Shadd 78.9 (15)