As the debate about universal pre-kindergarten heats up, it bears listening to one of our nation’s pre-eminent researchers, David Berliner.
He writes:
There are some European citations about early childhood education that are often left out of the debate in the USA. But we use them in 50 myths and lies that threaten American public education (Berliner, Glass and Associates, 2014, Teachers College Press:
“One recent study by economists in the United Kingdom examined data from the international test called PISA, the Program for International Student Assessment (seeMostafa & Green, 2012). They used data from the United Kingdom and Sweden, both of which had extensive programs of early childhood education, but the programs were not universal. That is, among the 15-year-olds tested in 2009, about 30% had not attended preschool. Not surprising, when they were younger, participation in early childhood programs was correlated with social class. The children of wealthier families, throughout the Western world, participate in preschool education at high rates. The researchers asked what the effects would have been on PISA literacy scores if all the children had gone to preschool, not predominantly those from the higher social classes. Their conclusion? In the United Kingdom, students in the lowest social class grouping benefited from preschool on average by an increase of 9.2 points on the PISA test, while those in the top social class grouping benefited by 5.5 points. Similarly, in Sweden, individuals in the lowest social class grouping benefited from preschool by an increase of 7.8 points on PISA, while those in the top social class grouping benefited on average by 4.1 points. Universalizing preschool apparently helps all children, but it helps the poorest children the most. These researchers estimate that the United Kingdom would have improved 12 ranks and Sweden would have improved 7 ranks, had their nations had universal preschool.
Green and Mostafa (2011) found that in all of the 34 countries in the European Economic Community, students at 15 years of age who had attended pre-primary education for more than 1 year outperformed those who did not, by an average of 54 points! Even after controlling for social background, attending preschool for more than 1 year increased performance on average by 33 points. These researchers found no strong evidence that early childhood education reduced inequalities in performance between those who were high and those who were low in social class standing. As a function of attending high-quality preschool programs, all students score higher on academic measures over a decade later. These researchers also discovered that in most countries high-quality preschool allowed more people, particularly women, to be employed. From their research they estimate that a 10% increase in availability of high-quality day care leads to a 6.1% increase in female employment, providing both a boost for the economy and a reduction in payments for unemployment.”
If we are in an international race to achieve excellence in educational achievement, perhaps data from other countries should be part of the discourse!
Diane Ravitch's blog 
First of all, we know that PISA is crap, so I’m not really sure why we should put much stock in those results. Here are a couple of good links discussing why they’re virtually worthless:
http://zhaolearning.com/2014/03/23/how-does-pisa-put-the-world-at-risk-part-3-creating-illusory-models-of-excellence/
http://zhaolearning.com/2014/03/29/how-does-pisa-put-the-world-at-risk-part-4-misleading-the-world/
Even if we accept the PISA data as valid, however, this study is flawed because it suffers from selection bias. Poorer families who ensure their children go to preschool tend to be the kinds of families that regularly instill values that lead to academic success. Poor families who don’t get their kids into preschool disproportionately don’t teach those same values.
Once you understand the issue in those terms, it is easy to explain both the achievement gaps between groups of poorer kids and why that achievement gap is larger than for wealthier families (i.e., even wealthier families who don’t put their kids in preschool likely transmit many of the values necessary for academic success).
As much as I respect much of David Berliner’s work, the reification of test scores and academic performance are the problems in current “discourse” about education.
The problem is acute in the US and becoming a pre-occupation in almost every developed nation (about 30).
The emphasis on scores on academic tests is really pathetic, a symptom of the tissue-thin thinking that urges policy makers and policy shapers to rely on test scores on academic tests as indicators of educational excellence in education if not predicates for a nations economic wellbeing, political stability, and the rest.
Few nations today rise or fall on the proportions of citizens who function only or primarily as academics and experts in taking tests–test where the questions are asked by others, the answers are known, and usually machine-scorable.