It was not immediately clear how the Bible would be taught or what instructional standards around it would require.

Oklahoma’s state superintendent on Thursday mandated that all public schools teach the Bible in a move that he said was meant to impart “historical understanding,” but that critics say blurs the constitutional boundary between church and state.

“The Bible is a necessary historical document to teach our kids about the history of this country, to have a complete understanding of Western civilization, to have an understanding of the basis of our legal system — and is frankly, we’re talking about the Bible, one of the most foundational documents used for the Constitution and the birth of our country,” superintendent Ryan Walters (R) said while announcing the policy.

It was not immediately clear how the Bible would be taught or what instructional standards around it would require. A memo to Oklahoma school districts from Walters’s office said schools “are required to incorporate the Bible, which includes the Ten Commandments,” into curriculum for fifth through 12th grades, effective immediately.

The move comes a week after Louisiana Gov. Jeff Landry (R) signed a law directing all public schools in the state to display the Ten Commandments, religious and ethical directives handed down to the prophet Moses in the Bible. Opponents have sued to stop the statute’s implementation. Like Walters, proponents of the Louisiana effort said having the Ten Commandments in classrooms is necessary in teaching history.

In his memo, Walters wrote that Oklahoma’s mandate “is not merely an educational directive but a crucial step in ensuring our students grasp the core values and historical context of our country.” He said the state’s Education Department may supply teaching materials for the Bible “to ensure uniformity in delivery.”

“Immediate and strict compliance is expected,” the memo said.

Tensions are mounting over the boundary between church and state, and the role religion should play in schools — if any. Days after the Louisiana Ten Commandments mandate, the Oklahoma Supreme Court rejected a proposed state-financed Catholic charter school, saying the first-of-its-kind religious public school violated the state and U.S. constitutions. Meanwhile, more than a dozen states have introduced bills to put chaplains in public schools. And as school voucher programs expand rapidly in Republican-run states, most of the funds — billions in taxpayer dollars — are directed to religious schools.

The efforts are proliferating at a time when the more conservative Supreme Court has expanded the rights of religious people and chipped away at precedent meant to keep the government from endorsing religion.

On Thursday, critics of Oklahoma’s new requirement called the move unconstitutional.

“Requiring a Bible in every classroom does not improve Oklahoma’s ranking of 49th in education,” Oklahoma state Rep. Mickey Dollens (D) said in a statement, referring to a recent report. “The State Superintendent should focus on educating students, not evangelizing them.”

Americans United for Separation of Church and State, a nonprofit that advocates for the disassociation of religion from government, signaled that it is prepared to fight the directive. The group is also among those challenging Louisiana’s Ten Commandments law.

“Americans United will do everything in our power to stop Christian Nationalists like Ryan Walters from trampling the religious freedom of public school children and their families,” Rachel Laser, president and CEO of the advocacy group, said in a statement. “This nation must recommit to our foundational principle of church-state separation before it’s too late. Public education, religious freedom and democracy are all on the line.”

Walters has been a prominent voice of conservative politics in Oklahoma, and the classrooms under his jurisdiction have been a common battleground. He denounced a teacher for perpetuating a “liberal political agenda” after she helped a student access banned books, and he endorsed disputed videos that teach conservative values in public schools.

Joseph Fishkin, a law professor at the University of California at Los Angeles, said that a moralistic teaching of the Bible in public schools would violate existing First Amendment law. If challenged, though, he said the Supreme Court “has moved recently so far to the right on this specific set of issues, of church and state.”

In 2022, the Supreme Court ruled that Maine cannot bar religious schools from receiving public tuition grants, elevating concerns about religious discrimination above constitutional worries about the separation of church and state. That same year, the court ruled in favor of a Washington state football coach who knelt at midfield to pray and was joined by student-athletes, tossing a long-established precedent that determines whether a law violates the Establishment Clause of the First Amendment.

This has inspired conservative groups and leaders to test the line, Fishkin said.

“It’s an effort to push against long-established boundaries and see where the court system will overturn the precedents,” he said.

It’s unclear how Oklahoma’s mandate would fare in the courts, if challenged, Fishkin added.

“It’s not like this is some untested question,” but due to the court’s recent shifts, everything is a little uncertain right now, he said.