I have been talking to my daughter about universal preschool. It is a concept that I both accept and understand. SOME children really need preschool. Those children are at one end of the spectrum or the other. One set are the children of the uneducated. Those children are not gaining enough vocabulary to achieve in school. One report I read said that a child from an uneducated household (they used poor- but we all know there are educated poor households) often come to school with between 1-3,000 words of understanding.
An educated household's child (they used professional) often comes to school with 15,000 to 20,000 words.
Who will learn to read quicker- the child who approaches the word "duck" and sounds it out OR the child who has seen a duck, watched it swim and quack, and THEN learns to read "duck"?
The other set who does well in preschool is usually a child of a very "advantaged" household- that does not have the time to spend giving the child lots of interaction....so they get it at preschool.
My own watching is that children who have SAHM or very intense child care families often have children who come to school with plenty to work with. They, if they have the intelligence, can usually go to a "good university" if they desire to check the blocks for it.