There are three scaffold scenes overall in The Scarlet Letter. The first is in chapter 2, when Hester is on public trial for her crime of adultery. Hester, though being haraungued by the crowd and by Dimmesdale to give up the name of her illegitimate child, refuses to implicate anyone. She is sentenced to 3 hours of solid public humiliation and a lifetime of wearing the letter "A" on her chest. What the crowd does not know is that Dimmesdale, the town minister and the man brow-beating Hester for a confession, is actually the father of her child. His hypocrisy is what makes this scene so dramatic for Hester. She does not cave or beg for forgiveness. The town looks down on Hester and doesn't bother to hide their disapproving glares and comments.
In the second scaffold scene (Chapter 12), it is night. Reverend Dimmesdale has been struggling with the guilt of his and Hester's situation for a about 7 years now. He hates himself for treating her like he has and is drowning in guilt, loneliness, and regret for not coming out in the first place. This internal conflict centers around his indecision in regards to coming clean. He wants to tell the town that he is the man with whom Hester committed her crime, that he is Pearl's father, and that he has been lying to all of them all this time. He does not because he feels a sense of duty to the townspeople as their minister. If they can't have faith in him, he feels they will have faith in no one. Unable to bear the pain of his guilt any longer, he goes out in the middle of the night to the scaffold where Hester was punished and "confesses" to the no one that is there. Eventually, Hester and Pearl walk by and they join him on the scaffold. Twice Pearl asks him if he will be willing to confess to the public someday and twice, he gives a definite "no." Pearl feels rejected. Then, many things happen at once. A meteor lights up the sky in what looks like the letter "A" and Chillingworth appears out of nowhere, looking in on this private family scene. He eats it all up, of course.
The differences between the first two scaffold scenes are many. First, the picture of the scene - day vs. night, crowded vs. empty. Also, this time it is not Hester who is being punished by Dimmesdale. It is Dimmesdale. Her guilt vs. his. Pearl is older now - old enough to understand who Dimmesdale is and why she wants so badly to hold his hand.
By Chapter 23, Dimmesdale is at the end of his rope. After his epic sermon, he drops to the ground and begins to die. As he is dying, he confesses. Pearl is thrilled that he finally offers her his hand in public, but Hester is peeved because she will be left, yet again, to deal with the consequences alone. However, she supports his confession, after which he drops dead. He has been released from his guilt, which had become his life. This differs because, obviously, now everyone knows the other guilty party.