There seems to be an assumption that a child will gain from state-funded preschool.  As usual, the state wants us to believe that they can raise our children better than we can, and it’s only for the state’s gain—for the taxpayer, it’s more public employees who are babysitting these kids to pay almost 100K, and the politicians who advocate state-run babysitting get backed by teachers’ unions, so they stay in office.
Little ones need to feel loved, number one.  Even if they enter state schools at six, they thrive academically.  My son’s an engineer and didn’t know his alphabet till he was six.  He wanted no part of learning his letters, but once he started, there was no stopping him.  He read, over and over, the Tolkien trilogy at the age of seven.  But he began school in Tokyo where his father and I shopped for schools because it was a free market.
That’s the answer, a free market, so parents can shop for good schools, and it will force these huge conglomerates we call our state-run education to improve; not using little children as pawns for the advantage of public employees and politicians.