Corrected entry: In the scene where Josh first plays in the Metropolitan Chess Club, he sits down across from the bearded man and they begin a speed game. Josh makes a final, crushing move with the white queen, after which the bearded man knocks over his king. But you can see that the bearded man is playing with the white pieces. So how can they both be playing white?
Corrected entry: In the scene where Josh and Jeff are playing the game for the championship, Jeff is pondering whether or not to bring out the queen. He does, and moves the queen to the left side of the board. A few moves later, Jeff takes the queen. However, Jeff takes it from the center of the board, and Josh never moved the queen back from the side.
Correction: Doesn't excuse the mistake but it's Jonathan not Jeff.
Corrected entry: In the movie, the final game (the National Elementary Championship) ends in a win for Josh. In real life, the game ended in a draw.
Correction: Not a mistake. That's how the director wanted to end the movie. This might belong in trivia.
Correction: Josh is playing with black. Josh's "crushing move" is actually the capture of the man's white queen, as the piece is slammed down off of the playing board.