Imagine you have a class of 25 students, and the parents of each one of them have their own ideas about how the teacher should — or should not — lead a lesson on the Rev. Martin Luther King Jr.'s “I Have a Dream” speech.

Each parent or set of parents proceeds to email, call, text or show up at school to discuss with the teacher their view of the lesson. Some demand that the lesson be posted online (a practice some state legislators want to mandate). Children tell their parents about the lesson and those who are unhappy complain to the teacher, possibly the principal, the superintendent and the school board, and may organize protests.

Now consider how many lessons a teacher teaches in a day. And let’s note that some classes have many more than 25 students, especially now, when classes are being doubled in many schools because of teacher shortages.

Of course, all parents won’t weigh in on every lesson, and they won’t do it every day, but the result would still be untenable for any school.

“It’s absurd for parents to tell teachers what to teach,” said Diane Ravitch, an education historian and advocate for public schools. “The result would be chaos, and in most cases would be parents telling teachers to teach the way they were taught decades earlier.” What’s more, she said, “It thoroughly discredits the teacher’s professionalism and expertise,” adding: “I can’t think of a more effective way to demoralize teachers and drive them out of the classroom.”

That, essentially, is the practical outcome of the “parental rights” outcry now being sounded in the media, at school board meetings and in politics. It has become a big issue in the Virginia governor’s race between Democrat Terry McAuliffe and Republican Glenn Youngkin.

This is the latest chapter of a decades-long movement in which parents try to dictate what public schools teach, fueled in part by “AstroTurf” groups created to look like they are grass-roots efforts by concerned parents to push the message.

The “parental rights” cry was heard, for example, after the Supreme Court ruled in 1954 that racial segregation of children in public schools was unconstitutional. “This same frenzy occurred after desegregation when educators tried to add Black achievements to school texts,” said Leslie Fenwick, dean emerita of the Howard University School of Education and dean in residence at the American Association of Colleges for Teacher Education.

“White parents burned books, physically threatened White teachers who tried to teach the more inclusive curriculum, and pressured school boards not to adopt books and curriculum that featured anything Black, by asserting that doing such was a divisive and communist trick,” said Fenwick, who was a leading candidate to be President Biden’s education secretary.

Aside from the implementation issues of parents dictating school lessons, there is the question of whether they have the right to do so, as supporters claim.

They don’t, according to education historians, including Jack Schneider, associate professor of education at the University of Massachusetts at Lowell, leader of the Beyond Test Scores Project and co-host of the “Have You Heard” podcast with freelance journalist Jennifer Berkshire.

“The ‘parents’ rights’ movement would be easy to misread as a response to some kind of overstep by the schools. But that isn’t it,” Schneider said in an email. “Parents have never had control over what the schools teach, and they have often contested particular approaches to teaching science, history, literature, and even math.”

Instead, he said, what’s happening “is that right-wing organizers are pushing this message in a cynical bid to score political points.”

“They’ve capitalized on the fact that many White parents are opposed to discussions about race, just like they seized on the use of masks in schools as a wedge issue,” he wrote.

Fenwick said: “The school curriculum is nearly all White in content and imagery. This is wrong and unhealthy for the intellectual and social development of children and youth. The more inclusive the school curriculum, the more likely students are to have an expansive understanding of the world and its diverse peoples.”

But that’s not what some parents want.

Schneider and Berkshire — who co-write the book “A Wolf at the Schoolhouse Door: The Dismantling of Public Education and the Future of School” — wrote about parents’ rights in public education in a piece in The Washington Post, saying that courts have given “great authority” to parents “when it comes to deciding how to raise and educate their children.”

“This right, however, does not mean that public schools must cater to parents’ individual ideas about education,” they wrote. “Parents can opt out of the public system if they wish, and pay to send their children to private or religious schools. But even there, parental rights remain subject to state regulation and override.”

The subject has become an issue in the Youngkin-McAuliffe gubernatorial race. At a Sept. 28 Virginia gubernatorial debate, Youngkin said that school systems should better inform parents about what is being taught, saying that some parents in Fairfax County were upset about “sexually explicit material” in a school library. “You believe school systems should tell children what to do,” he said to McAuliffe. “I believe parents should be in charge of their kids’ education.”

McAuliffe, who was previously governor of Virginia from 2014 to 2018, responded: “I’m not going to let parents come into schools and actually take books out and make their own decision. … I don’t think parents should be telling schools what they should teach.” He then said that he gets “really tired of everybody running down teachers.”

McAuliffe’s comments were referencing legislation he vetoed in 2016 and 2017, which would have notified parents of sexually explicit content in education materials. The bills would have required teachers to provide alternative materials to students whose parents objected to the content.

McAuliffe said he vetoed the bill because the Virginia Board of Education was considering changing state policy to accommodate parents’ concerns. The state board decided that local district school boards should set the policy, not the state.

The National Coalition Against Censorship — a group of organizations representing writers, publishers, teachers and civil liberties groups — had written to the state board of education warning that any such requirement would be unconstitutional and “would effectively create a parental consent requirement for all students, including some who are not minors, to read educationally valuable materials that contain some sexual references.”

Schneider warned that public schools survived previous culture wars “because both sides recognized the importance of publicly funded and publicly minded education.”

But that consensus is disappearing. “We need to pay attention, then, not just to what this means for electoral politics, but also to what it means for education,” he said. “If enough Americans can be convinced to turn on their schools, the right will be all too happy to wipe public education off the map.”