John Engler attends a panel discussion at the Washington Post. (Dayna Smith/FOR THE WASHINGTON POST)

The head of the country’s second-largest teachers union and a business leader who tried to weaken unions as a onetime governor of Michigan have made a joint plea to the nation’s governors to stand by the controversial Common Core academic standards.

Randi Weingarten, president of the American Federation of Teachers, and John Engler, who leads the Business Roundtable and served as Michigan governor from 1991 to 2003, have written to governors in 45 states — as well as the mayor of the District of Columbia — that have fully adopted the new K-12 math and reading standards.

Weingarten and Engler urged the governors to “get it right” by giving educators time and support as they make wholesale changes in the way they teach and to hold off on testing students on the new standards until schools have fully implemented new curricula based on the standards.

And the pair asked the governors to stand behind the Common Core standards in the face of a growing backlash from critics on the right, the left and in academia.

“We ask you to stay the course and oppose attempts to impede the successful implementation of the Common Core State Standards,” Weingarten and Engler wrote in their Nov. 26 letter to the governors. None of the governors responded.

Written by a group of governors and state education officials, with endorsements from the federal government and funding from the Gates Foundation, the Common Core standards are designed to prepare students for an eventual career or college.

“This came from the bottom up, this didn’t come out of Washington,” said Engler, who called the standards an “economic and moral imperative.”

Increasingly, high school graduates have been unprepared for college; recent studies have found that up to 40 percent of first-time undergraduates need at least one remedial course in English or math.

On a recent well-regarded international exam, U.S. teenagers scored average in reading and science, and below average in math, compared to 64 other countries and economies that participated. Organizers who administered the 2012 Program for International Student Assessment said they expected that the new Common Core standards would increase the academic achievement of U.S. students.

Participating states are introducing the standards in classrooms nationwide. They are expected to begin testing students on the standards in the 2014-15 school year. Most states plan to use the scores on new tests to evaluate teacher performance.

In a country with a long history of local control over education, the Common Core standards mark the first time that nearly every state has agreed to one set of skills and knowledge. The idea is that all students should possess certain skills by the end of each grade, so that a first-grader in Maryland will learn the same skills as a first-grader in Maine or Montana.

The standards are not curriculum, as it is up to each state to decide what and how to teach.

Opponents range from tea party activists who say the standards amount to a federal takeover of local education to progressives who bristle at the emphasis on testing and the role of the Gates Foundation. Some academics say the standards are too weak; others say they are too demanding, particularly for the youngest students.

Republican governors in several Southern states recently have been fielding challenges about the Common Core standards from conservative activists. When new sessions begin in statehouses next month, legislators in several states are expected to debate the standards.

On Monday, Mississippi Gov. Phil Bryant (R) issued an executive order, saying that the state will retain complete control over curriculum and testing, despite the fact that it adopted the Common Core standards. States that have adopted the standards already retain control over those matters, but Bryant felt a need to make an explicit statement.