For more than a generation, educators and policymakers have been agonizing about America’s achievement gap, the persistent chasm in academic performance between poor and privileged children.

A new book and a national campaign launched Thursday says the country must pay equal attention to the “opportunity gap” — which exists when poor and minority students and English-language learners lack the same access as affluent students to skilled teachers, quality curriculum and well-equipped schools.

Instead of just placing a heavy emphasis on “outputs” of the educational system — test scores and graduation rates — the nation also must focus on “inputs,” or what it invests in schools, said Stanford University’s Linda ­Darling-Hammond, one of 20 academics who contributed to the book, “Closing the Opportunity Gap.”

“We’re not saying, ‘Don’t pay attention to outcomes,’ ” Darling-Hammond said. “If you want to achieve the outcomes, and not just talk about them, you have to pay attention to inputs.”

The book, funded by a grant from the Ford Foundation, argues that the accountability movement that began in earnest with the 2002 No Child Left Behind law placed too much emphasis on testing students and measuring outcomes. Under that federal law, schools for the first time were required to test students in math and reading in grades 3 through 8 and once in high school, and to make progress each year in scores or face a series of escalating penalties.

“We’ve done a good job in the last decade of calling attention to the achievement gap,” said ­Darling-Hammond, who has advised President Obama on education issues. “But what we haven’t been doing is addressing some of the fundamental reasons for the achievement gap: the poverty and segregation sets up some kids to have less when they get to school, and then the funding inequities, so that when they get to school, they don’t have the resources and instructional supports that we want and need them to have.”

The campaign, funded by the Schott Foundation for Public Education, will encourage state policymakers to consider ways to ensure that schools serving low-income children have the same quality of teaching, curriculum and resources as that found in more affluent schools.

“We want to change the conversation,” said Kevin Welner of the University of Colorado at Boulder.

The campaign echoes a message similar to one offered in February by the Equity and Excellence Commission, a 27-expert panel convened by Congress to propose ways to improve public education for poor American children.

“Ten million students in America’s poorest communities . . . are having their lives unjustly and irredeemably blighted by a system that consigns them to the lowest-performing teachers, the most run-down facilities, and academic expectations and opportunities considerably lower than what we expect of other students,” the commission wrote. “These vestiges of segregation, discrimination and inequality are unfinished business for our nation.”

The notion of an “opportunity gap” has been gaining popularity in recent years.

At a meeting with black newspaper publishers last month, Education Secretary Arne Duncan decried that many African American students attend racially isolated schools that have low standards and not enough resources.

“This opportunity gap is deeply troubling,” Duncan said. “It is painfully at odds with the American creed: that if you study hard and play by the rules, you get a fair shot at the future, regardless of your Zip code, skin color or the size of your bank account.”

A student in a mostly minority school is much less likely to have access to classes in calculus and physics than a student in a mostly white high school, Duncan said. “Less than 8 percent of students taking AP mathematics or AP science courses today are African American. What sense does that make; how do unequal opportunities help close the achievement gap? Obviously, they don’t. Instead they actually perpetuate the gap.”

The administration’s proposed 2014 budget calls for universal preschool for all low-income 4-year-olds as one way to narrow the opportunity gap.

But Darling-Hammond said the federal government should do more. For instance, when it awards grants, she said, it could require states to show progress toward closing the opportunity gap.

Achieving this goal is not just about spending more money, Darling-Hammond said.

“It’s not just dollars, it’s how you spend the dollars,” she said. “We could all come up with examples of dollars poorly spent that didn’t make a difference. This is about laying out all the components of the opportunity gap and hoping that this is something policymakers are ready to deal with.”