Marilyn Sachs, groundbreaking author of titles in the early wave of realistic fiction for middle grade and YA readers, and a progressive social and political activist, died on December 28. She was 89.

Sachs was born Marilyn Stickle on December 18, 1927 in The Bronx, N.Y. She noted in her autobiography for Something About the Author that her childhood neighborhood bustling with children – including some who bullied her – was an inspiration for many of her books. She credits her desire to avoid bullying, and a rich family history of storytellers, as catalysts for developing a talent for “rearranging the truth” and telling tales, which served her well as a novelist.

Sachs had a fondness for reading and writing from an early age, and often took refuge from neighborhood hassles in the local library. After completing high school, where she served as editor of the school paper, Sachs wanted to attend college, though her father objected to the idea. She persisted, moving to Brooklyn where she supported herself with part-time jobs while studying at Hunter College. At the same time, she was becoming politically active, and met her future husband, sculptor Morris Sachs, when the two belonged to the progressive political organization American Youth for Democracy. The couple soon married, and after she graduated from Hunter in 1949, Sachs took a job as a children’s librarian trainee at the Brooklyn Public Library. She worked there for a decade while earning her master’s of library science degree at Columbia University. But she also had begun entertaining thoughts of being a professional writer. “I loved my job, most of the kids, and the books,” she said in an interview, “I read and read and read, and somewhere along the line I realized what kind of books I wanted to write and who I wanted to write for.”

Sachs took a leave of absence from the library in 1954 to focus on her writing. She completed her first novel during that time, Amy Moves In, about “a [poor Jewish] girl named Amy who told lies,” as Sachs once described it. Though she shopped the manuscript around, editors in those days were not interested in a realistic story of a family going through hard times. Sachs temporarily set the book aside, and with her husband and their two young children made a cross-country move to San Francisco, where Sachs worked part-time at the San Francisco Public Library. In 1963, a former colleague from her days at the Brooklyn Public Library got in touch with Sachs, letting her know that she had become a book editor, and inquiring about the Amy manuscript. With that, Amy Moves In had finally found a home and was published by Doubleday in 1964 to favorable reviews.

For the next 20 years, Sachs published roughly a book a year, writing “in between childhood sicknesses, peace marches, flooded toilets, and all the other demands life made on my time,” she said in her autobiography. In 1968, with four titles already under her belt, she became a full-time writer. Among the books from that early period is the middle grade novel Veronica Ganz (Doubldeay, 1968), featuring a tomboy character that Sachs has said was “a composite of all the bullies who terrorized me as a child.” The novel was named an ALA Notable Book. Her 1971 novel The Bears’ House (Doubleday), about a family of neglected children struggling to survive, was a finalist for the 1972 National Book Award. Sachs’s acclaimed YA novels include The Fat Girl (Dutton, 1983), which tackles issues of body image and social status. Sachs was a co-editor, with her longtime editor Ann Durell, of the anthology The Big Book for Peace (Dutton, 1990), which provided proceeds to peace organizations, and enabled her to combine her children’s book and activist passions.

She went on to write more than 40 books for young people, more recently the 2005 novel Lost in America (Roaring Brook), which is a sequel to her novel A Pocket Full of Seeds (Doubleday, 1973), about a French Jewish girl who must fend for herself when her family is taken away by the Germans during WWII.