It's a huge difference. As soon as a kid can read, they can learn in a way that isn't just you telling them stuff. They can self-direct their learning, read books about stuff, go online and devour Wikipedia, etc. It's not just "hey, can anyone not read a newspaper by the time they leave school?", it's "how soon does this kid have the tool to satisfy their natural curiosity about things that require more than someone telling them about it?" which establishes their relationship with learning itself, with knowing how to learn.