There are several differences between the novel The Blind Side and the film adaptation. The most important structural difference is that the novel has two parts, one focusing on student and football player Michael Oher, and the other on the history of American football in general. The film focuses entirely on Michael Oher's story, enhancing the melodramatic elements. In this way, the film humanizes the characters by ignoring the historical elements of football.
Another difference is that the film arguably focuses more on the Tuohy family as opposed to the Michael Oher story. Critics of the film explain that by framing the story from the perspective of an upper-class white family, the viewing audience can be more emotionally manipulated to accept the story of a homeless black student who becomes a successful football player. While the novel used Michael Oher's story as a backdrop to examine football and cultural race relations in regards to sports, the film tells the story without historical context.
...Lemming tried to reach the kid by phone. He found out that his surname was pronounced "Oar," but that's about all he learned. He was accustomed to the social lives of high school football stars... this kid not only had no handlers, he didn't appear to exist outside of school. He had no home; he didn't even have a phone number. (Lewis, The Blind Side, Google Books)
"[In the film] some of Leigh Anne’s friends wonder if she is helping Michael out of a sense of “white guilt,” a notion she laughs off without entirely dispelling."
(A.O. Scott, "Two Films..." nytimes.com)
This criticism explains that the underlying themes of race relations, the depiction of a realistic world and characters versus idealized versions, and the way history and culture affect the acceptance of varying social groups is eliminated or at least diminished in the film. In contrast, the book is heavy with football jargon and history, and might not be as easily absorbed as the simpler film. Many more differences, especially in the fictional aspects of the film, are present, and show the marked divide between educational historical novels and entertaining films.