Updated at 12:15 p.m. ET.
Arne Duncan will step down as President Obama's education secretary in December, a White House official confirms to NPR.
Obama has selected Deputy Education Secretary John B. King Jr. to replace Duncan. King is a former New York State education commissioner. (President Obama is making a personnel announcement at 3:30 p.m. ET.)
King is 40 years old, and the White House says that would make him one of the youngest Cabinet members in American history. (Julian Castro, the current secretary of Housing and Urban Development, is 41.)
Duncan has been there since the beginning of Obama's tenure and is one of only a few members remaining from Obama's original Cabinet.
He's come under fire at times from the right and left because of various initiatives, including Race to the Top, the Common Core educational standards and an embrace of charter schools — something that has rankled teachers unions.
The irony of the controversies is that education was one area in which Republicans, early on in Obama's tenure, would say they agreed with him. They liked his reform agenda and Common Core originated with Republican governors like Louisiana's Bobby Jindal who have since backed away seeing an uproar from conservatives and even some teachers.
Duncan is moving back to Chicago, where he said, in a farewell letter to colleagues, that he has been splitting time. Duncan is the former head of Chicago schools.
In the letter, Duncan called the opportunity to serve as education secretary "the greatest honor of my life." He endorsed King as his successor and included this reflection King wrote about his upbringing.