Preschool is Good, Right?

WND has the whole article here, but the most telling quote is below.

On average, the report finds that the earlier a child enters a preschool center, the slower his or her pace of social development, while cognitive skills in pre-reading and math are stronger when children first enter a preschool program between the ages of 2 and 3.

While I won't argue the point about slower social development, I will call BS on the claim to 'stronger cognitive skills in pre-reading and math'. If this was the case, we'd be seeing improved math and reading scores from the PS since we are now graduating kids young adults that had pre-school social conditioning prior to their formal schooling. Right?

Instead we see a steady decline in literacy rates and math scores (unless you make the testing easier). If pre-school offers a tangible benefit, where is it? Are our PS so bad that they squander it? Could be, but I doubt that pre-school offers any benefit at all, other than a guilt free (at least if you don't think about it) day care.