When the News was on when they first were talking about Calvin, and the Calvin character is 14 years old. The News reporter says "He's Lean, he's mean, he's 13." She says he is 13, when really he is 14.
When Calvin's special sneakers are first delivered he immediately puts on of them on and looks at the initials on the inside tongue of the shoe. The bully then walks over to Calvin sitting on the ground and grabs the shoes, which are no longer on Calvin and are now tied together.
During Calvin's initial game with the Spurs, the scoreboard reveals that Calvin has only 12 points heading into the final possession. Therefore, the game-winning three pointer would increase his total to 15, yet the following day the news anchor says that Calvin had 27 points.
When Calvin is paying Tracy in the 1 on 1, he has 60 seconds to score and win the prizes. The clock starts counting down immediately when Calvin is handed the ball when it should not have started until Calvin actually put the ball in play.