At the party, when Rachel slaps Melinda after learning that Melinda called the cops, Rachel's hair is straight. However, when Rachel gets into the car with her friends that are trying to escape, her hair is curly.
When Melinda tells Rachael about the rape, she is wearing two orange shirts, and the next day when Rachael confronts Andy, Melinda is seen wearing a different, long sleeved orange shirt. However, when Melinda talks to her father on the front porch she is back in the two orange shirts again.
The movie came out in 2004, but the book it is based on came out in 1999. So the turn of the century for the book would be the 1900s. For her extra credit assignment, Melinda is told to write an essay on a cultural influence at the turn of the century. Yet the movie takes place at the turn of the 21st century, around 2003. It should have specified "turn of the last [20th] century." She decides to write about the suffragists of the 1910s.
"Melinda says the school mascot is changing from the Trojans to the Hornets. However, during the pep rally the cheerleaders are introduced as the "Merryweather Falcons"." This isn't a goof, it's a running theme through the movie as a later announcement changes the team name to the Wombats.