When the choir first experiments with hip-hop, the clock behind the convict's head changes between shots. Sometimes it moves up to five minutes ahead, sometimes it moves backwards.
Johnson's tattoo disappears when he sings in the church.
In the competition, the tall convict with the high pitched voice is handcuffed when he comes to the front of the stage. Moments later, he is dancing with one arm in front of him and one behind his back. From his sideways position, that would be impossible.
During the final performance, the convict with the high-pitched voice is singing, with no cuffs or chains. Later, during the credits, his restraints are on.
Near the end of the film, Lilly passes her and Darrin's new baby over to her grandfather for him to hold while they go perform. However, in the shots of the crowd behind Darrin, both the grandfather and the baby are nowhere to be seen.
When the two main characters are talking as children, the boy mouths the girl's line when she says she wants to marry Michael Jackson.
At the end of the scene where the choir sings, "Rain Down", Darrin mouths "Call His name" when the rest of the choir sings "Praise His name".