A Lesson Before Dying is told in chronological order with very little rewinding or fast-forwarding. It starts at the start, and finishes at the finish. It doesn't try anything sneaky like flashbacks or foreshadowing.
However, there are a few little fancy stylistic flourishes that sneak in there to keep us on our toes. For example, when we suddenly start reading Jefferson's Diary, we have to wonder where this fits into the straightforward story that's been chugging along so far:
mr wigin you say rite somethin but i dont kno what to rite an you say i must be thinkin bout things i aint telin nobody an i order put it on paper but i dont kno what to put on paper cause i aint never rote nothin but homework i aint never rote a leter in all my life cause nanan use to get other chiren to rite her leter an read her leter for her not me so i cant think of too much to say but maybe nex time. (29.1)
There's a huge contrast between Grant's narrative style and Jefferson's. This throws readers for a bit of a loop. But one thing that adding in this very different perspective does is confirm everything that Grant has been trying to tell us. His students are not learning, and no one expects much of them.
The overall effect of this stylistic curveball is that it gives us some proof: we can believe what Grant tells us. Jefferson's diary proves that Grant's students aren't learning how to line-edit.
But the insertion of Jefferson's diary in A Lesson Before Dying also does something else: it proves that history is as much to blame for Jefferson's less-than-stellar spelling. Education was denied to slaves, and, eighty years later, the education available for black children in Louisiana is still horrifically bad. In many cases (like Jefferson's) the adults have less education than the children.
It's through Jefferson's letter, though, that we see a glimmer of hope. Jefferson's not going to win any spelling bees, sure. But his spelling is better than his nannan's spelling: she was basically illiterate. Change is occurring—it's occurring at a glacial pace thanks to racism and prejudice, yes—and there is hope for the future of not only education, but of all facets of black Louisianans' lives.