When Landon and his friends leave the hallway to go to class in the shot behind Landon, you see that Belinda is clinging onto Landon's arm, not fitting in their character relationship. (Mentioned in the director/actor commentary: Shane West says that they were all good friends and left the scene naturally. They didn't realize they were being filmed at the time.)
When Jamie receives the paper from Landon to a star he had named for her, she is clearly holding the paper as she moves to sit down. As soon as she is seated, the paper is completely missing from the scene. (This is revealed by the director's commentary on the DVD.)
After the play ends, Landon is being congratulated by Eddie. As Eddie is talking, Jamie leaves the theater and we see Eddie cross in the front of the shot. But he's supposedly talking to Landon at the time and in the very next shot, he's standing in front of Landon talking again.
After the school play Landon is talking to his father. During the last shot of Landon we see a young man walk behind him in a green button up shirt with a white shirt underneath. In the next shot, the same man walking down the stairs toward them again.
The day after the play, Landon goes through the library to go to the cafeteria, he has a white shirt and blue vest on. When he goes into the cafeteria, he is wearing a white tee shirt under a green shirt. Then when he is with Eric later, he is wearing the blue and white outfit again.
When Landon and Eric are practicing Landon's lines at Landon's house the Azaleas (surrounding them) are in full bloom. Later, when Landon speaks with his mom at their house about Jamie having faith in him (after Jamie told him she loved him), the Azalea blooms on the same Azalea bushes have died - most have fallen off and a few brown blooms remain. Several scenes later, when Belinda comes and apologizes to Landon for the hurtful fliers, again at Landon's house, the same Azaleas (now surrounding Belinda and Landon) are once again in full beautiful bloom. Azaleas are perennials, only blooming once per year for about 2 weeks.
When Jamie is crossing the school yard carrying a box, and one of the girls says, "Nice sweater," to her, Jamie is wearing a backpack, as evidenced by the visible straps on her shoulders. When she walks away we see her from the back and she is not wearing a backpack.
During the school play, just after Landon says, "Will you sing for me?" the camera is facing Jamie and the piano begins the song. We see Landon's hand touching her elbow, and as she is about to sing, she puts her arm on the table, pushing his hand out of the way. The camera then cuts to the view from the piano, and you can see that Landon's arm is resting by his side on the table.
When Landon first walks into the hospital to visit Clay he is wearing a green, checkered button-up shirt and when he enters the room he is wearing a totally different shirt with a grey t-shirt underneath. However, when he goes to the a second time to visit Jamie, when she is able to go home, he is wearing the same green shirt he wore when he entered the hospital to see Clay. It seems that the first shot where he walks in the hospital to see Clay should be put in this scene.
When Jamie is in the hospital and is giving Landon her mother's quote book, in the first shot from the front she first reaches for it with her right hand. In the second shot from the back, she is reaching for it with her left hand while her right hand is stationary. In the last shot from the front she has the book in her right hand and gives it to Landon.
At the beginning of the movie, when Landon and Clay are on the tower before Clay jumps into the pool, the water is spraying out over the water like a regular high diving tower, however, when the tower is seen from below, there is a small stream of water, not a spray
When Landan walks into the living room at the end of the movie, the wedding picture is on the table next to the couch. The next scene it is on top of the piano, then in the next scene it is back on the table again.
When Landon goes after Dean in the cafeteria (after the flyers are passed around) Dean takes the paper and makes a crack about Jamie. Landon grabs the paper back from him but in the next shot when he shoves Dean, the paper is not in either of their hands.
The day that the flyer is made about Jamie, all of the characters are wearing exactly the same clothes as they were a few days before when Dean asked Landon if they were still cool. A few days later, when the fliers come out they all have the same clothes back on.