As printed textbooks increasingly gather dust in classroom bookshelves, a new and expansive survey published on Thursday finds that social studies teachers are turning to digital sources and primary documents from the nation’s past.

While the most popular curriculum providers are not ideologically skewed, the report warned about a trend of “moralistic cues” in some left-leaning school districts, with lessons that seemed to direct students toward viewing American history emotionally, as a string of injustices.

In conservative areas, the report said laws restricting the teaching of “divisive concepts” had been “extremely corrosive of teacher morale and detrimental to the integrity of good history teaching.”

Still, the report, from the American Historical Association, found that history teachers overwhelmingly affirmed the goals of presenting “multiple sides of every story” and depicting U.S. history as “a complex mix of accomplishments and setbacks.”

The survey paints an unusually detailed portrait of how the nation’s history is being taught during an era of intense political polarization. It reached 3,000 middle and high school teachers across nine states: Alabama, Colorado, Connecticut, Illinois, Iowa, Pennsylvania, Texas, Virginia and Washington.

Nicholas Kryczka, a research coordinator at the American Historical Association and an author of the report, said that overall, the survey suggests that most educators understand the need to exercise self-restraint on political issues.