Clara Luper, an Oklahoma schoolteacher and civil rights stalwart who led one of the first in a wave of sit-in campaigns that helped desegregate lunch counters across her home state and the South, died June 8 of undisclosed causes at her home in Oklahoma City. She was 88.

In August 1958, 18 months before a group of black students won national attention for demanding service at segregated restaurants in Greensboro, N.C., Mrs. Luper led a handful of children into the Katz drugstore in downtown Oklahoma City. They sat down and ordered Cokes.

The waitress refused to serve them. White customers spit on them and cursed. But Mrs. Luper and her young compatriots — members of the NAACP youth council, ages 6 to 17 — stayed for hours.

“I knew I was right,” she told the Daily Oklahoman years later. “Somewhere I read, in the 14th Amendment, that I was a citizen and I had rights, and I had the right to eat.”

She and the other sit-inners returned for several days, said her daughter Marilyn Hildreth — who was an 8-year-old participant in the protest — before the drugstore agreed to serve them sodas and hamburgers.

“Within that hamburger was the whole essence of democracy,” Mrs. Luper said in 1988.

Katz eventually desegregated all 38 of its stores in Oklahoma, Missouri, Kansas and Iowa.

Over the next several years, Mrs. Luper and the NAACP youth council members took their campaign to drugstores and restaurants across Oklahoma City. Mrs. Luper endured death threats and jail — she was arrested 26 times during protests — but she and her group succeeded in pressing for the desegregation of more than 100 establishments.

In an interview Monday, Marilyn Hildreth attributed the protestors’ success in part to their youth.

“It’s very difficult as an adult to do wrong to children,” she said.

The Oklahoma sit-ins received scant national attention. But civil rights activists across the country noticed Mrs. Luper’s success, and sit-ins became a common tool for forcing peaceful change.

“As Rosa Parks was to the integration of buses, Clara Luper was to the sit-in movement,” UCLA psychiatrist Louis Jolyon West, who co-authored a 1966 study of the psychology of children who had participated in sit-ins, wrote in the New York Times in 1990. “Regrettably, her leadership never received the recognition it deserved.”

In Oklahoma City, Mrs. Luper’s efforts helped lead to the city council’s 1964 passage of an ordinance prohibiting racial discrimination at stores, swimming pools and other public accommodations.

A native of Okfuskee County, Okla., Clara Mae Shepard was born May 3, 1923, and raised in a segregated community. She graduated from Oklahoma’s Langston University in 1944 and received a master’s degree in history from the University of Oklahoma in 1951.

She began her teaching career in 1948 and taught history at Oklahoma City high schools for more than 40 years.

Her first marriage, to Bert Luper, ended in divorce.

Her second husband, Charles P. Wilson, died in 2010.

Survivors include two children from her first marriage, Marilyn Hildreth and Calvin Luper; a daughter from her second marriage, Chelle Wilson; a sister, Oneita Brown; five grandchildren; eight great-grandchildren; and one great-great-grandson.

Mrs. Luper’s sit-ins were rooted in a 1957 trip to New York City, where her students were invited to perform a play she had written about the Rev. Martin Luther King Jr.

A bus ferried the group north across an invisible line to cities where Mrs. Luper’s students were allowed to eat at lunch counters next to white customers. “It gave my young people a taste of freedom,” Mrs. Luper told a reporter in 2002.

On the way home, they recrossed that invisible line, returning to a South and its “Whites Only” signs. Once home, they resolved to do something to change Oklahoma City.

At a NAACP youth council meeting, Mrs. Luper’s daughter Marilyn suggested they all go sit somewhere until they were served.

“I thought about my father who had died in 1957 in the Veterans’ Hospital and who had never been able to sit down and eat a meal in a decent restaurant,” Mrs. Luper recalled in her 1979 memoir, “Behold the Walls.”

“I remembered how he used to tell us that someday he would take us to dinner and to parks and zoos. And when I asked him when was someday, he would always say, “Someday will be real soon,” as tears ran down his cheeks. So my answer was, ‘Yes, tonight is the night.’ ”