The on-time graduation rate for all D.C. high school students ticked up two points to 61 percent this year, according to data released Thursday by the Office of the State Superintendent of Education.

That’s a far less dramatic change than last year, when the rate dropped nearly 20 points after the federal government began requiring the city — and all states — to calculate graduation rates with a new and more rigorous formula.

The District’s citywide average masks a big difference between its two school sectors.

D.C. Public Schools ticked up three points to 56 percent this year. Meanwhile, public charter schools’ average graduation rate fell slightly but, at 77 percent, remains quite a bit higher than DCPS.

Chancellor Kaya Henderson said the two systems can’t be fairly compared. Charter schools can require commitments from students, she said — such as attending summer school or extended-day programs — that traditional public schools don’t have the ability to demand.

And DCPS schools often end up serving the students who didn’t want to (or couldn’t) keep up with the rigorous expectations of some charter schools, she said.

Assertions that charter schools benefit from self-selected student populations is a matter of frequent and heated debate. OSSE is in the midst of studying data that show how students move between DCPS and charter schools, and maybe their report — expected soon — will shed some light.