Were the books, "Push" and "Precious" by Sapphire based on a true story or person?

From an interview with Sapphire:

But the story is not autobiographical, she says. "The level of abuse I suffered is not nearly as extreme as in the book, and there is no character in the story, not even the teacher, who is based on me." Rather, Precious is a composite character, she says, created from the real-life stories she encountered while teaching for seven years, from 1987 to 1993, in an adult-literacy programme in Harlem.