The Economist has an article here detailing the advantages of President Obama’s call for universal preschool.
Getting poor children into high quality preschool programs can have many benefits for the families of these children as well. Parents will be freed up to work. The enrichment that the preschool children receive (early teaching of letters, field trips, learning how to play cooperatively, a love of stories and reading) may spill over to their siblings as well. Parents will have the opportunity to see what an enriched environment for children looks like.
As to the gentleman who commented no innovations have made the slightest difference in educational outcomes, I would just say that the country needs to get serious about developing a love and habit of reading in children. But this is a start. A good start, I think.