The article reports on a survey of early childhood educators done by a group called Defending the Early Years. It's not a scientific study, mind you, but it does give voice to educators who worry about the reforms brought on by current policy.
They report on shifts in early childhood education that result in children hating school. With the increased focus on "academic" skills, children exhibiting more anti-social behavior. Many public schools report large increases in serious negative behavior.
They point out (and I have seen) that privately funded schools for the richest and most privileged classes in the US provide play-based learning for young children.
Here at my kindergarten I try to keep learning as happy and as play-based as possible given the current climate of reform.
I commend the article to you. Here's the link: Disturbing Shift