Joan Countryman stepped down as head of the prestigious all-girls Lincoln School on Providence’s East Side a year and a half ago, saying that after a dozen years, she was ready to enjoy retirement, her family and her summer home in Little Compton.

Retirement didn’t last long.

On Wednesday, Countryman, 66, boarded a 14-hour flight to Johannesburg, South Africa, to start her new job — running a new $40-million school for girls started by Oprah Winfrey. The Oprah Winfrey Leadership Academy will open Tuesday. The television talk-show host and billionaire known for her philanthropy has said that founding the school “is the best thing I have ever done,” and has personally overseen every detail of the project, from the construction and decoration of the campus’ 26 buildings, to hiring the 16 faculty and selecting the uniforms, clothes, dishes and silverware the students will use.

“When I got the call, I said there are not many things I am saying yes to these days,” Countryman said in a phone interview as she waited to board her flight at Dulles Airport in Virginia. “But how could I say no to a school in South Africa for poor girls?”

A friend who heads an independent school in California contacted Countryman about six months ago. She asked if Countryman would serve as a consultant for Winfrey’s ambitious plan to start an all-girls boarding school in a village, Henly-on-Klip, one hour south of Johannesburg. The school would strive to educate the complete person — intellectually, spiritually and emotionally — and would give poor girls an opportunity to gain leadership skills and help shape the future of their country.

Intrigued, Countryman flew to South Africa in August and helped to interview some of the girls being considered for the inaugural class of seventh and eighth graders. In the end, 152 girls were chosen, and the school plans to add a class each year until it reaches 450 students in grades 7 through 12.

Countryman also met Winfrey for the first time.

“I was impressed with how she interviewed the girls,” Countryman said. “She could bring out all sorts of lively, interesting reactions.”

The two discussed the future of the school.

“I suggested they use a structure similar to what we have at Lincoln, which is a head of school and then principals who run different parts of the program,” Countryman said. Winfrey liked the idea.

The women also discussed the importance of having a South African educator run the school.

“At some point she said she wanted someone like me. But I said that I was retired,” Countryman said.

In the end, Countryman agreed to take over as interim head of the academy, with the understanding that she would help to find a permanent headmistress. Countryman said she expects to spend about six months getting the school up and running and identifying a successor. She will continue to serve as a consultant.

“The main thing is to have a school that is appropriate for South Africa,” Countryman said. The students speak 11 languages and come from varied cultural and religious backgrounds. English will be the official language of the college-preparatory school, but students will be required to learn one or two indigenous languages, such as Zulu, Countryman said.

All the students are poor; many have parents who have died of AIDS and some have been sexually assaulted. In an article in the January issue of O The Oprah Magazine now on newsstands, Winfrey, 52, said she identified strongly with the girls and women of South Africa when she has visited there over the years. A close friendship with Nelson Mandela moved her to offer to found a girls school there. Winfrey, the primary backer of the school, said she expects to spend a total of about $50 million on the project.

Oprah, who was reared by her grandmother, grew up poor in Mississippi and was sexually abused starting at the age of 9.

“When I became successful as a journalist, I knew that it was a part of me to give back to girls who are like myself,” Winfrey said in the magazine article. “I’ve carried that dream since I was 20.”

Countryman also describes the Leadership Academy as a dream come true, and one she could not pass up.

“For me, it was a wonderful chance to be in a country I’ve always been interested in and felt challenged by,” Countryman said. She had visited South Africa twice before, and said her children, Rachel and Matthew Countryman, were both involved in anti-apartheid and divestment campaigns in the 1980s. “When Nelson Mandela was released and then elected president, it seemed like a dream. I never thought that would happen in my lifetime. I also never thought I’d be able to use my skills as a school leader to help poor girls in South Africa. That seems like another dream.”

Countryman, a Quaker, began her career first as a math teacher and then as an administrator at a Quaker school she had attended as a student, the Germantown Friends School in Philadelphia. After graduating from Sarah Lawrence College in 1962, she worked in the civil-rights movement and later received a master’s degree in urban studies from Yale. In 1966, Countryman received a Fulbright fellowship to the London School of Economics. She is credited with revitalizing Lincoln School’s Quaker values and diversifying the school’s faculty and student body during her tenure.

Countryman said she and Winfrey discussed the kind of environment girls need to flourish.

“This school is not a religious school, but the idea in Quaker schools that you have a deep respect for the dignity of every person, that resonates in South Africa, with its mixtures of traditions and cultures,” Countryman said. “They have 11 official languages and they affirm the importance of what that represents in terms of cultural diversity.”

Breaking the news to her husband, architect Ed Jakmauh, her children and her four grandchildren was easier than Countryman expected.

“I just had to say ‘Oprah’ and they said, ‘Go!’ ” she said. “Everyone, including all those little girls in Africa, has heard of Oprah.”

The school officially opens Tuesday, as South African schools run from January through December, with vacations in April, August and December. Countryman says her family will visit her in the coming months.

“When I interviewed one of the little girls, I asked her if she had any questions. She said no, but ‘please tell Oprah thank you for the opportunity,’ ” Countryman said. “So that’s what I’m feeling right now. Thank you for the opportunity, for building a school for girls who otherwise would not have this chance.”