A dozen years ago, Betsy Sawyer formed a creative writing club for fifth-graders she taught at the Groton-Dunstable Regional Middle School — a group that became much more than an after-school project.

“She was my teacher and I adored her, so I joined,’’ said Clara O’Rourke, who was 10 then and is now about to graduate from Clark University in Worcester. “We were just going to write our own book or do creative projects.’’

Under Mrs. Sawyer’s guidance, the fifth-graders who joined the Bookmakers and Dreamers club planned and created a gigantic volume of essays, poetry, and artwork called “The Big Book: Pages for Peace.’’ Among its 3,500 contributors are the Dalai Lama, Nelson Mandela, and Oprah Winfrey.

The 12-year project was unveiled at a fund-raiser at the John F. Kennedy Presidential Library and Museum in Boston in 2014. In March, it began a worldwide tour, starting at the United Nations. Mrs. Sawyer and three of the club’s original members went to New York to speak at the opening ceremony.

By then, Mrs. Sawyer was in late stages of leukemia and she entered a hospital with an infection and fever upon arriving in New York. Against the advice of doctors, she spoke at the UN ceremony. Mrs. Sawyer died two weeks later, on April 3, in her home in Shirley. She was 60.

While speaking at the UN, “she was so vibrant and happy, just like a little girl,’’ said her husband, Charlie, who accompanied Mrs. Sawyer to the ceremony along with other family members.

This month, the book will be displayed at an international peace conference in South Korea.

O’Rourke said club members got the idea for the 1,000-page book when they passed around a copy of the “Guinness World Records’’ book. They discussed trying to break a record and found an entry about the world’s smallest book. The fifth-graders wanted to try to create the world’s biggest book.

“Mrs. Sawyer never said, ‘That’s a crazy idea,’ ’’ O’Rourke recalled. “She said, ‘Let’s do it. But if we’re going to create the biggest book, we have to come up with a really big topic.’ ’’

That weekend Mrs. Sawyer saw reggae singer Jimmy Cliff in concert. When he asked the audience what they had done lately to help promote peace, she knew she’d found that topic.

Each year, members of the club — which grew to include hundreds of children — met weekly to write letters asking people to send their views on world peace and how to achieve it. Responses poured in.

“My grandmother wrote a letter and the Dalai Lama wrote a letter,’’ O’Rourke said. All were included in the book, alongside notes, poetry, and artwork by the children Mrs. Sawyer taught.

Many original club members, whom Mrs. Sawyer called the Peacemakers, are now on the verge of careers aimed at making the world a better place, said O’Rourke, who works for the Worcester Public Schools researching accommodations for English language learners. She said the project taught her that “world peace is about making sure people are comfortable and happy, and not living in a state of fear or poverty or violence.’’

When Mrs. Sawyer first mentioned “The Big Book,’’ her husband said, “it sounded so complicated that it didn’t seem possible. But anytime my wife spoke about this project, she just lit up. And you knew that she would somehow accomplish it.’’

Rosemary Elizabeth Guercio was born in Fitchburg, the daughter of Leonard Guercio and the former Mary Ward. Her parents nicknamed her Betsy after Betsy Ross because she was born on Flag Day. At age 12 she began working at the Bull Run in Shirley, the restaurant her father opened in 1946.

After graduating from what is now Ayer Shirley Regional High School, Mrs. Sawyer enrolled at the Culinary Institute of America in Hyde Park, N.Y., and graduated with a degree in baking. Returning to the Bull Run, she made the restaurant’s bread and desserts. Soon after she married chef Charlie Sawyer, who was 20 years her senior. Because of their age difference, her father refused to go to the wedding.

“Betsy was upset, but she understood it,’’ her husband said. “It was what she expected. She said, ‘He’ll come around in a while.’ And he did, just like she said, three years later. Then he hired me back as a chef.’’

After their children were born, Mrs. Sawyer decided restaurant hours weren’t suited to motherhood and set out to become a teacher. She worked as a preschool and kindergarten assistant while pursuing a degree in elementary education at what is now Fitchburg State University. She later received a master’s in English literature at the University of Massachusetts Boston, writing a thesis on the letters of poet Elizabeth Bishop.

While finishing her master’s, she was teaching, raising three children, and dealing with breast cancer that was diagnosed when she was 30, and which resulted in a double mastectomy. All that, plus traveling from Shirley to the UMass Boston campus in Dorchester “was a real slog, a very great effort for her,’’ said Lloyd Schwartz, her professor and thesis adviser.

“She had so much on her plate, but damned if she wasn’t going to finish that thesis,’’ said Schwartz, who also penned a contribution to “The Big Book.’’

“Betsy was one of the gutsiest and most determined people I ever met,’’ he said, “and one of the most modest.’’

Mrs. Sawyer, who started the club soon after beginning teaching at Groton-Dunstable, was “like a kid herself with her wide-eyed optimism and this indomitable spirit,’’ O’Rourke said. “She had expectations that went beyond our wildest dreams. She made us go beyond the beyond.’’

As her fifth-graders amassed letters from Maya Angelou, Jimmy Carter, Senator Edward M. Kennedy, Michael Douglas, skateboarder Tony Hawk, and others, Mrs. Sawyer oversaw the book’s production.

She procured special paper and convinced a company to donate large-size printing capability and ink. A group of ­UMass Lowell students designed and built a page-turning device for the book, which measures 12 by 10 feet and weighs more than 2,000 pounds.

Ultimately the project didn’t set a world record because someone else created a book with bigger dimensions. But sharing the book’s message at museums and embassies around the world eclipsed the club’s original plan.

“I just wanted a writing club,’’ Mrs. Sawyer told the Globe in 2011. “To see what it’s grown into — I don’t think anybody really understands the magnitude.’’

An avid reader who loved to swim and ski, Mrs. Sawyer was “very fun and very funny,’’ said her son Bryan of Shirley, who manages the Bull Run. “In the best way, rules didn’t really apply to my mother. She was always one to push the envelope.’’

A service was held at the Bull Run, where Mrs. Sawyer long ago carved the words “ ‘Betsy Guercio was here’ a million times’’ onto a barrel table “in a deeply notched, all-capital notation we treasure today,’’ said her sister, Alison Tocci of Shirley.

In addition to her husband, son, and sister, Mrs. Sawyer leaves two daughters, Kate and Alison, both of Shirley; two brothers, Peter and Chip Guercio, both of Shirley; another sister, Dede Recko of Shirley; a stepdaughter, Trish Sawyer-Bourgoin of Abington; and four grandchildren.

“That girl was just a whiz, a ball of fire, and she was the strongest and most unselfish person I ever met,’’ her husband said. “She really packed everything into finding ways to help others. And anybody who ever said no to Betsy, well they were just wasting their time.’’

Kathleen McKenna can be reached at kmck66@verizon.net.