The North Carolina school board on Thursday encouraged teachers to use multiple sources when teaching American history, not just the curriculum written by a Koch-funded group.

In December, the state approved a curriculum for a new history course on the “Founding Principles.” The state hired the Virginia-based Bill of Rights Institute, which is funded in part by the conservative Koch brothers, to write a curriculum for the course.

The North Carolina Department of Public Instruction then encouraged teachers to use the curriculum document drafted by the Bill of Rights Institute.

But on Thursday, the Department of Public Instruction approved a new document for teachers to use, which draws on multiple sources, in addition to the guidelines from the Koch-funded group, according to the Associated Press.

State schools superintendent June Atkinson told the AP that teachers were always allowed to use multiple sources when teaching the course.

“The big idea is that teachers are the people in our state charged with selecting materials to teach the standards,” she said.

The decision by the state in December followed the controversy over the new AP U.S. History exam, which conservatives have criticized as too negative.