Minneapolis Public Schools officials said they failed to vet literacy training materials that some teachers complained showed racially and culturally insensitive stereotypes.

Earlier this month, some teachers received training for a new early-literacy curriculum. They received “Little Books” that they could use to teach literacy skills to kindergarten through second-grade students.

But the books contained images that teachers found offensive. A book titled “Lazy Lucy” showed a young black girl on the cover, and another book called “Nieko, the Hunting Girl,” featured a picture of an American Indian girl and her father.

“Due to staffing shifts and the desire to get a program in place for the new school year, the books were not comprehensively vetted,” interim Superintendent Michael Goar said in a statement. “We now know this was a mistake. We regret that this happened. We will do better.”

The books were part of a larger curriculum that the district purchased in July from a Utah-based company called Reading Horizons. The district paid the company $1.2 million.

District officials say they immediately pulled the books after teachers complained, and no students had received the materials. They also say they have asked Reading Horizons to write new books.

“Teachers will be central to that conversation,” Minneapolis’ Chief Academic Officer Susanne Griffin said. “These revisions won’t just be for Minneapolis, but for districts across the country.”

Reading Horizons officials did not return messages seeking comment Thursday. On the company’s Facebook page, officials apologized and vowed to change the content of their books.

“It would be a shame for anyone to avoid our products while we work to resolve our weakness and work to better represent a variety of cultures,” the company wrote.

Goar said the district will continue to work with Reading Horizons. “This program has been successful in improving student outcomes across the country, including outcomes in diverse districts like ours,” he said.