In July 2014, the nation’s second-largest teachers union passed a cheeky resolution urging President Barack Obama to put Education Secretary Arne Duncan on an “improvement plan” that would walk back five years worth of gains by the nation’s schools.

The resolution called for Duncan to abandon his “failed education agenda” in favor of one endorsed by unions — more money, fewer tests and less accountability.

If Duncan didn’t “improve,” he should resign, the American Federation of Teachers said.

But Duncan was doing exactly what Obama wanted him to do, and he kept doing it. More than a year later, when Duncan began making plans to step down, Obama tried to talk his friend and basketball buddy into staying. When that failed, Obama chose a replacement much like Duncan, who will return to Chicago in December.

Education is one of the few issues on which Obama has been willing to buck the unions who helped elect him twice. That was clear from the minute he nominated Duncan, an innovative risk-taker who pushed pay-for-performance and charter school expansion in seven years as CEO of Chicago Public Schools.

Duncan has had plenty of conservative critics, too. They say he fancied himself the nation’s superintendent, substituting his judgment for that of states, local school boards, teachers and parents.

Congress wasn’t happy, either, that Duncan found ways to move his education agenda forward while lawmakers were busy not reauthorizing the federal No Child Left Behind Act.

That agenda: Raise academic standards for students and measure their gains through rigorous testing. Hold teachers accountable for their students’ progress. Promote charter schools, giving parents an alternative when their local schools aren’t performing.

The states didn’t have to go along with it, but Duncan had some tools with which to encourage them. He launched Race to the Top, inviting states to compete for $4 billion in federal stimulus money by adopting reforms. Later, he offered to waive some sanctions prescribed by NCLB if struggling schools took steps outlined by the Department of Education.

Want those federal grants? Adopt the nationwide curriculum guidelines and get out of the way of charters. Want to avoid forced restructuring of failing schools? Tie your teacher evaluations to student performance.

Many states resisted adopting the Common Core standards, and several have since ditched them.

Yet Duncan can point to modest but measurable progress. The U.S. graduation rate is at an all-time high of 81 percent. More Latino and African-American students are graduating and entering college.

His departure presented Obama with an opportunity to placate the unions in time for the 2016 elections, but no. John King, deputy secretary of education, will be acting secretary. He founded a charter school in Massachusetts at 24 and later helped launch a network of charters in New York. He’ll stay the course.

“Arne’s done more to bring our educational system, sometimes kicking and screaming, into the 21st century than anybody else,” Obama said last week. “None of this change has been easy, and we still have a long way to go.”