To put it mildly, she thinks very little of it. To expand on that a bit, she finds it overly rigid and parochial (though even Scout probably wouldn't use that word yet), as well as a simple waste of time. Think of how the system (in the person of Miss Caroline) reacts when Scout already knows how to read. She says "…tell your father not to teach you any more. It's best to begin reading with a fresh mind" and refers to his teaching as "damage." This is Atticus she's talking about!
While she grows more accustomed to it, it is clear that Scout's mind is too big for this limited formal system; she learns more by her free reading, her time with Calpurnia, her games, and, of course, Atticus.