what does "scaper"mean? is it also dialect? what is the correct spelling of this word?
"We'd best to go by the Glen springs and see has he come out and watered there."
"A big ol' doe watered there today," Jody said. "Whilst I was asleep. I built me a flutter-mill, Pa. It run fine."
Ma Baxter stopped the clatter of her pots and pans.
"You sly scaper," she said. "That's the first I knowed you been off. You gittin' slick as a clay road in the rain."
He shouted with laughter.

Question

what does "scaper"mean? is it also dialect? what is the correct spelling of this word?
"We'd best to go by the Glen springs and see has he come out and watered there." 
"A big ol' doe watered there today," Jody said. "Whilst I was asleep. I built me a flutter-mill, Pa. It run fine." 
Ma Baxter stopped the clatter of her pots and pans. 
"You sly scaper," she said. "That's the first I knowed you been off. You gittin' slick as a clay road in the rain." 
He shouted with laughter.

Answer

Scaper in this context is actually meant "a person who escapes." This is not proper english, but in the book you're reading it was done on purpose to show that they were not educated. From the looks of it, the english they use is referred to country or red-neck english.