Dana Goldstein makes it:
Any radical rethinking of American public policy ought to start with a consideration of one of our most politically neglected populations: The majority of 3-to-5-year-olds who have no access to high-quality, low-cost educational options. As scientists have learned more about the brain, they've concluded the early years are the most crucial ones for cognitive development. Seventy-five percent of middle-class kindergarteners can write their own names, compared to just about half of poor kindergartners. The typical middle-class 5-year old can identify all 26 letters of the alphabet on her first day of school; a 5-year old living in poverty may know only two letters. By first grade, middle-class children have double the vocabulary of their low-income peers.
All these early literacy skills are associated with success in elementary school and beyond: Third-graders who aren't proficient in reading are four times less likely than proficient readers to graduate from high school.