The effects of preschool have been studied and showed no benefits after grade 3. Not sure about the year round portion of it, but it seems to me this is a narrative born from intuition and not from evidence.
I've heard these studies referenced before, but studies have limitations and I wonder if there is some form of early childhood education that can lead to statistically meaningful improvements down the road, just not approaches that happen top have been studied.
As I understand it, it's the gaps in the summer that account for the gaps in education. That's Gladwell's assertion. When kids have gaps without learning at an early age, they fall behind quickly and it is devastating.