Ron Singer, who is 67 and a member of the Navajo Nation, called it three years of “pure hell.” At age 7, he was sent to a Native American boarding school run by the federal government in Tuba City, Ariz., more than 40 miles from his home.

“It was like a prison setting,” he said, with 40 boys confined to a dormitory at night and made to march around the school like soldiers by day. Children who misbehaved were told to pull down their pants and then beaten, Mr. Singer said.

“I can still feel the hurt,” he said.

President Biden formally apologized on Friday for the abuses that generations of Native American children suffered at the schools, calling the mistreatment “one of the most horrific chapters in American history.”

For more than 150 years, from the early 1800s to the late 1960s, the federal government removed thousands of Native American children from their homes and sent them to hundreds of boarding schools across the country.

The schools were designed to erase the children’s tribal ties and cultural practices. Children were given new names, forcibly converted to Christianity and punished for speaking their Native languages. Many were physically and sexually abused.

A report released in July by the Interior Department identified by name nearly 19,000 children who attended the schools between 1819 and 1969, though it acknowledged that there were more. At least 973 children died at the schools and were buried at 74 sites, 21 of which were unmarked, the report said.