78,000 3-year-olds were enrolled in KG in 2009
I'd bet significantly more than my traditional shiny new nickel that virtually every one of those 78,000 kids are "parent misunderstood the question" or other data quality issues.
A good chunk of the apparently-young-for-grade kids may be in California, or other late-cutoff states. The December 31 cutoff (vs August / September in much of the country) means that a 5yo-in-October 1st grader hasn't been skipped.
I'm quite surprised (to the extent that believing data quality is a significant concern) that 1-2% of kids in every grade from 2nd on up are either double-skipped or single-skipped in a state with a late cutoff.
