When did tom say, I done it? What effect did it have on Becky?

Tom said, "I done it!", when the school master questioned Becky about the torn book. Becky's eyes were shining with gratitude.

Tom stood a moment, to gather his dismembered faculties; and when he stepped forward to go to his punishment the surprise, the gratitude, the adoration that shone upon him out of poor Becky's eyes seemed pay enough for a hundred floggings.