The plot is a combination of the Sarah Dessen novels "Someone like You" and "That Summer." The first novel is the story of Halley helping Scarlett through the results of her interaction with Michael. The second novel is the story of Haven, whose parents have broken up and whose sister is planning a wedding. The stories were combined, with Dessen's approval, by reassigning Haven's family to Halley.
Mandy Moore cut her hair short because she felt it suited the role; the movie producers weren't happy about it. In the end they compromised and had her wear hair extension for some of the movie and then have her having her hair cut put into the film.
Mandy Moore later starred in Saved! (2004), which also deals with her high school classmate getting pregnant.
Allison Janney: [mother] This is one of numerous movies where Janney plays a neurotic or disturbed mother.