Half the story is no less a lie for being half right.
High quality EC programs help low SES kids in the first few grades.
You can see the effects on high school graduation rates and in college attendance.
But ...
Many EC programs aren't "high quality."
They have few to no effects on middle and upper class kids. They are there, after all, to make up for inadequacies in the families that the kids are born into. It's politically dangerous to say that those families are inadequate. But in terms of education and school culture, they are.
By 5th or 6th grade, most of the effects of the high-quality EC programs have vanished. You can still see the effects, given a large sample size and the right stats and the right datasets, on high-school and college attendance rates.
A lot of the payback isn't with the kids' education itself. The researchers narrow and widen their research and criteria as needed to prove their point (hard "science" seeks disconformation of their hypotheses, social science usually keeps looking until it finds support). A lot of the benefit is keeping the kids out of harm's way. It's providing them with food and shelter. It's providing the low-income parents with free day care so they can keep their jobs and provide better for their families. But it's always sold as "education."
There'd be far more actual "education-based" payback if the EC programs were cut in half and the savings put into "middle childhood" programs. Because the families that failed the kids by age 5 aren't going to just pick up the slack, by and large; they're going to continue to fail the kids when they're 9 and 10 and 14 and 15. We can't do that, however, because a lot of the discussion is disengenuous. It's about feeling good, paying lip service to a cause, then achieving the actual goals that the programs are billed as providing. Even if the programs did *nothing* except warehoused, clothed, and fed the kids, we'd still be pushing for them. We know that their educational benefits are temporary, with trivial results 10 years later, yet we trumpet the trivial as essential. Let's just sell them as what they are: federal daycare for both low-income parents as well as those who shouldn't be parents.