The current fashion is for teachers to be a “guide on the side, instead of a sage on the stage,” he says, quoting the latest pedagogical slogan, which means that teachers aren’t supposed to lecture students but to “facilitate” learning by nudging students to follow their own curiosity. Everything Mr. Hirsch knows about how children learn tells him that’s the wrong approach. “If you want equity in education, as well as excellence, you have to have whole-class instruction,” in which a teacher directly communicates information using a prescribed sequential curriculum.

Mr. Hirsch, 92, is best known for his 1987 book, “Cultural Literacy: What Every American Needs to Know.” It is an argument for teaching “specifics,” followed by a lengthy list of them—thousands of historical figures, events, concepts and literary works with which, in Mr. Hirsch’s view, educated Americans should be familiar. Heavily weighted toward Western history and civilization, the list provoked charges of elitism. Yet Mr. Hirsch is singularly focused on helping disadvantaged kids. They “are not exposed to this information at home,” he says, so they’ll starve intellectually unless the schools provide it.

He continues the argument in his new book, “How to Educate a Citizen,” in which he describes himself as a heretofore “rather polite scholar” who has become more “forthright and impatient because things are getting worse. Intellectual error has become a threat to the well-being of the nation. A truly massive tragedy is building.” Schools “are diminishing our national unity and our basic competence.”

Mr. Hirsch is nonetheless cheerful in a Zoom interview from a vacation home in Maine, his armchair perched next to a window with a water view. An emeritus professor at the University of Virginia, he normally resides in Charlottesville, where he continues his research and acts as the chairman of the Core Knowledge Foundation.

He cites both history and neuroscience in explaining how education went wrong. It began in the 1940s, when “schools unbolted the desks and kids were no longer facing the teacher.” Instead children were divided into small groups and instructed to complete worksheets independently with occasional input from teachers. “That was also when our verbal test scores went down and the relative ranking of our elementary schools declined on a national level.” On the International Adult Literacy Survey, Americans went from being No. 1 for children who were educated in the 1950s to fifth for those in the ’70s and 14th in the ’90s. And things have only gotten worse. Between 2002 and 2015, American schoolchildren went from a ranking of 15th to 24th in reading on the Program for International Student Assessment.

The problem runs deeper than the style of instruction, Mr. Hirsch says. It’s the concept at its root—“child-centered classrooms,” the notion that “education is partly a matter of drawing out a child’s inborn nature.” Mr. Hirsch says emphatically that a child’s mind is “a blank slate.” On this point he agrees with John Locke and disagrees with Jean-Jacques Rousseau, who thought children’s need to develop according to their nature. Both philosophers make the “Cultural Literacy” list, but “Locke has to make a comeback” among educators, Mr. Hirsch says. “The culture is up for grabs, and elementary schools are the culture makers.”

Mr. Hirsch is a man of the left—he has said he is “practically a socialist.” But he bristles at the idea that kids should read only books by people who look like them or live like them. He recalls how reading outside his own experience enabled him “to gain perspective.” Growing up in Memphis, Tenn., in the 1930s, he says, “there was no one I knew who wasn’t a racist.” In his teens, he picked up Gunnar Myrdal’s “An American Dilemma: The Negro Problem and Modern Democracy” (1944), which “allowed me to escape.” The Swedish sociologist’s survey of American race relations “made a huge impact” on Mr. Hirsch. “I take it as an illustration of how important knowledge is and how important it is to not necessarily become a member of your culture.”

That’s no less true in 21st-century America. “The idea that identity and ethnicity are inborn and indelible from birth is a false view that leads to group hostility,” Mr. Hirsch says. “The idea that there can be an American culture that everyone joins seems to be anathema to some academic thinkers,” Mr. Hirsch says. “But I can’t believe it’s anathema to any normal person in the country who isn’t some social theorist.” It’s fine for children to embrace their particular heritage, he says, but also vital to create an “American ethnicity.” The purpose of elementary schools “is to make children into good citizens.”

That requires knowledge that is “shared nationally, if you’re going to read and write and communicate with one another.” He’s dismayed that people keep getting hung up on the particulars. “I’m fine with arguing about whether it shall be Toni Morrison or Herman Melville. Who cares?” He calls elementary school “a nonpartisan institution,” a view that may seem quaint in an era when schools are adopting ideological curricula like the “1619 Project” and teachers are displaying “Black Lives Matter” banners as their Zoom backgrounds.

Mr. Hirsch wants to correct some of these excesses. He dedicates “How to Educate a Citizen” to the late political scientist Richard Rorty, who died in 2007. Rorty “made a distinction between the political left and the cultural left,” says Mr. Hirsch, who considers himself a man of the former but not the latter. He commends to me a 1994 New York Times article, “The Unpatriotic Academy,” in which Rorty wrote: “In the name of ‘the politics of difference,’ [the left] refuses to rejoice in the country it inhabits. It repudiates the idea of a national identity, and the emotion of national pride.” Mr. Hirsch agrees and longs for the “willingness to sacrifice for the good of society that was very strong” during his early years. “Patriotism is important because we want to make our society work.”

Mr. Hirsch also takes issue with grade schools’ focus on “skills.” Whether it is imparting “critical thinking skills,” “communication skills” or “problem-solving skills,” he says such instruction is a waste of time in the absence of specific knowledge. He describes the findings of the National Academy of Sciences on the subject of the “domain specificity of human skills.” What this means, he explains in the new book, “is that being good at tennis does not make you good at golf or soccer. You may be a talented person with great hand-eye coordination—and indeed there are native general abilities that can be nurtured in different ways—but being a first-class swimmer will not make a person good at hockey.”

He cites the “baseball study,” conducted by researchers at Marquette University in the 1980s, which found that kids who knew more about how baseball was played performed better when answering questions about a text on baseball than those who didn’t understand the game—regardless of their reading level. The conventional response in education circles is that standardized tests are unfair because some kids are exposed to more specific knowledge than others. In Mr. Hirsch’s view that’s precisely why children should be exposed to more content: Educators “simply haven’t faced up to their duty to provide a coherent sequence of knowledge to children.”

There are now about 5,000 schools in the U.S. that use some form of the Core Knowledge curriculum, developed by Mr. Hirsch’s foundation. And research suggests Mr. Hirsch is right. A recent large-scale randomized study of public-school pupils in kindergarten through second grade found that use of the Core Knowledge Language Arts curriculum had statistically significant benefits for vocabulary, science knowledge, and social-studies knowledge.

Even in poor neighborhoods, kids at Core Knowledge schools perform well and are admitted to competitive high schools. From the South Bronx Classical Charter School to the public schools in Sullivan County, Tenn., Mr. Hirsch is clearly proud that his ideas have helped the least privileged kids in America.

He questions the idea that children who are exposed to more “experiences” are at an automatic advantage. “That’s what fiction is for,” he quips. And not only fiction. “The residue of experience is knowledge,” he says. “If you get your knowledge from the classroom, it’s just as good as if you got it from going to the opera. Poor kids can catch up.”

Asked about the effect of the pandemic and lockdown on children’s emotional well-being, Mr. Hirsch shrugs, then offers an anecdote from a principal at a Core Knowledge school. Before classes began one morning, a second-grade girl approached him and said: “I’m so excited for today.” When the principal asked why, she said, “Because today we are going to learn about the War of 1812.”

“Gee, I wonder what that’s about,” the principal said.

“I don’t know,” the girl replied. “But today I’m going to find out!”

For Mr. Hirsch, the lesson is clear. No matter the circumstances, “kids delight in learning things.”

Ms. Riley is a resident fellow at the American Enterprise Institute and a senior fellow at the Independent Women’s Forum.