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.
My children went to a Catholic school where the year before 1st grade was labeled K2 and the year before that K1, instead of "preschool". Many of the 78,000 3yo kids are probably in preschool labeled as "Kindergarten 1".
K1 in the Boston public schools is described at
http://www.countdowntokindergarten.org/bpsoverview.html .
ETA: Boston has a small number of "K0" seats "primarily for three-year-old children with special needs, but there are some general education seats in K0 classrooms so that the classes can be integrated."
