Claireece Precious Jones is an obese and illiterate 16-year-old girl who lives in Harlem with her abusive mother Mary. Precious has recently fallen pregnant with her second child, the result of being raped by her father, also the father of Precious' first child. The school has decided to send her to an alternative school because she is pregnant. Precious is furious, but the counselor later visits Precious's home and convinces her to enter an alternative school called Each One Teach One. Despite her mother's insistence that she apply for welfare, Precious enrolls in the school. She meets her teacher, Ms. Blue Rain, and fellow students Rhonda, Jermaine, Rita, Jo Ann, and Consuela. All of the girls come from troubled backgrounds. Ms. Rain's class is a pre-GED class for young women who are below an eighth-grade level in reading and writing and therefore are unprepared for high school-level courses. They start off by learning the basics of phonics and vocabulary building. Despite their academic deficits, Ms. Rain ignites a passion in her students for literature and writing. She believes that the only way to learn to write is to write every day. Each girl is required to keep a journal. Ms. Rain reads their entries and provides feedback and advice. By the time the novel ends, the women have created an anthology of autobiographical stories called "LIFE STORIES – Our Class Book" appended to the book. The works of classic African-American writers like Audre Lorde, Alice Walker and Langston Hughes are inspirational for the students. Precious is particularly moved by The Color Purple.
While in the hospital for the birth of her second child, a boy she names Abdul Jamal Louis Jones, Precious tells a social worker that her first child is living with her grandmother. The confession leads to Precious' mother having her welfare taken away. When Precious returns home with her newborn baby, her mother is enraged and chases her out of the house. Homeless and alone, she first passes a night at the armory, then turns to Ms. Rain who uses all of her resources to get Precious into a halfway house with childcare. Her new environment provides her with the stability and support to continue with school. The narrative prose, which is told from Precious' voice, continually improves in terms of grammar and spelling, and is even peppered with imagery and similes. Precious has taken up poetry. She's also eventually awarded the Mayor's office's literacy award for outstanding progress. This accomplishment boosts her spirits.
With her attitude changing and her confidence growing, Precious finds herself thinking about having a boyfriend, a real relationship with someone near her age, with someone who attracts her interest. Her only sexual experience thus far has been the rape and sexual abuse by her father and, to a lesser extent, her mother. Although she tries to move beyond the trauma of her childhood and distance herself from her parents, an unwelcome visit from Precious' mother reveals that her Father has died from AIDS. Testing verifies that Precious is HIV positive, but both her children are not. Her classmate Rita encourages Precious to join an incest support group, as well as an HIV positive group. The meetings provide a source of support and friendship for Precious as well as the revelation that her color and socioeconomic background weren't necessarily the cause of her abuse. Women of all ages and backgrounds attend the meetings. The book concludes with no specific fate outlined for Precious, with the author leaving her future undetermined.