Via Gary Sasse’s Twitter stream comes a post from the left-wing Brookings Institution suggesting that the evidence is mounting that universal pre-K may not only do no measurable good, but might actually do harm:

By the end of kindergarten, the achievement test boost for treatment group children in the consenting subsample [who had been in a government pre-K program] had disappeared. By the end of first grade, teachers rated the same children’s work skills and preparation as weaker than the control group; the effects reversed. By the end of second and third grade, control group children did better on academic tests than treatment group children.

As always, the question is why.  In this case, the study’s authors, Jeanne Brooks-Gunn and Ron Haskins, speculate that pre-K might make kids just too darn prepared for school, so they get bored or otherwise distracted when mixed with children who aren’t as well prepared.  In June, another study put forward the alternative speculation that the organized pre-K is actually worse for a significant portion of students than the alternative care that they would have received from parents, grandparents, or some other care provider who’s in it for the relationship.

Maybe the answer is some blend of the two.  It wouldn’t exactly be surprising if the best education for children at very early ages is extensive interaction with people who love them and mildly guided free play, which then becomes gradually more focused on learning as they progress through kindergarten and elementary school.  The pre-K kids might do better early on in kindergarten because they’re already trained in the basic classroom techniques that kindergarten teaches, but once the non-pre-K kids pick up those simple skills, their own developmental advantages begin to make the difference.  Or maybe it has more to do with parents, who’ve begun the natural emotional separation earlier.

Whatever the answer turns out to be, perhaps we should consider the possibility that this is an area too individual and personal to families for government to be meddling.  Of course, that would put an end to public-sector labor unions’ push for more government-mandated members.