I don't have children but I have little faith in our public school systems. When I was in first grade I had a terrible teacher. In second grade I was sent to our new Catholic elementary school. The nun gave a number of tests and then sent the kids home that passed them for a week (I didn't pass) and spent a week catching the rest of us up as best she could.
In seventh grade I was in one school system and a different one for 8-12. In the first school system American history went up to but did not include the Civil War that came in 8th grade. That next year I was in a new school system (same state) so no study of the Civil War they covered it the year before. In high school we had to take 2 years American History. So my first year the teacher only made it as far as just before the Civil War. The next year I had the other American History teacher who had covered through the Civil War in the part 1 class. What this boils down to is because of not standardizing classes across the country I never studied parts of our history until I went to college where I made sure I had the same teacher for both semester so that there were no gaps.
It seems to me that there are a lot of problems in the regular 1-12 classes that need to be dealt with before the question of mandatory pre-school even comes up.
What sort of problems. Class sizes, resources, a pay scale that gets truly dedicated teachers. Then there is the ever changing requirements for teachers. An example is my sister who majored in special education for her Bachelors and who also has a master in special ed. Then after 25 years of experience in elementary school special ed she is told she is no longer qualified to teach special ed students so they make her a math teacher. Then there is the growing problem of teachers who have inappropriate relationships with students. Or parents so uninvolved in their childrens lives that they have no idea if they do their homework, attend school etc.
My sister the teacher says one of the biggest problems facing education in this country is the lack of involvement of the parents. That when you call them in because the child is failing they blame the teacher. When the teacher responds that they aren't learning everything they need because they never do homework guess what the parents respond. It's your job to teach them and see they do whatever work is required. When she tries to tell them that she isn't at home with them that they as the parents have to see they do the homework they say they don't have time for it you deal with it it's your job. (She is a mother and says she literally has to bite her lip to keep from asking them why the hell they bothered to have children if they weren't going to be involved in their lives.)
So tell me how is spending billions of dollars on mandatory pre-school going to ultimately see that these kids aren't criminals, are more educated, can get better paying jobs etc. if the parents don't see to it that they do the work required to get the education. Face it pre-school is a glorified play group with a small amount of true educational benefit.
Of course this is my opinion based on my observations of nieces and nephews and friends children and what they tell me.