Story highlights "He's done more to bring our education system -- sometimes kicking and screaming -- into the 21st century more than anybody else," Obama said

Obama has selected Deputy Secretary of Education John B. King, Jr. to replace Duncan

(CNN) President Barack Obama praised Arne Duncan's service as secretary of education on Friday, hours after Duncan said he would step down in December.

"He's done more to bring our education system -- sometimes kicking and screaming -- into the 21st century more than anybody else," Obama said at a White House ceremony. "America is going to be better off for what he's done."

Duncan leaves the administration as the longest-serving education secretary in U.S. history, Obama said.

"It's a record that I truly believe that no other education secretary can match," he said. "Arne bleeds this stuff. He cares so much about our kids. And he's been so passionate about this work."

While speaking about the impact his parents -- both educators -- had on him, Duncan got emotional.

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