H.S.
Dear J.,
Pre-school is becoming very regimented and even pushing on "standards." Personally I do not think children need this. They need time to develop socially, emotionally, and also in fine coordination before they are required to sit and letter and do dittos. I think you should see if their are some other mom's with kids his age in your area that don't go to pre-school and then get together...even "organize" a little group that you take turns doing activities such as play dough, letter recognition...in a fun way..like stringing Cheerios and talking about words that start with "O". Some schools are more nurturing and creative. Some parks have preschool setting. I would see if you can to find a preschool that has mothers volunteering as assistants (we took turns) and there is one credentialed teacher. We had one at a church near us.
Regardless of whether you son goes to pre-school, you will have to make sure he is ready for Kindergarten. Two of my three boys I kept back so they were 6 when they stated Kinder. (An Aug BD...but fine hand coordination was not in and I knew they pushed lettering) and (A June BD...he was a premie..very small for his age). I think it helps with maturity, especially in boys. I have worked in the school system and had to convince parents to retain and repeat Kindergarten so the child could mature.
Also just spending time at the park with other mom's and kids helps socially. Do hand coordination tasks with him at home...bead stringing, play dough, simple dot-to-dots, coloring. Read a lot to him...that is very important...he will learn to sit and listen...ask him questions so he will think about what you have read.
Do not fret not being able to afford preschool. Stay at home moms are the best for preschoolers. If he has to wait out one more year for kindergarten to mature, it might be a good thing for him.
H.
P.S. I read the other responses and my sons are now a professor in college, a doctor in a cardiology fellowship, and a financial analyst. If you want a good education, make sure they get to go to a private high school in prep for college. Preschool is not going to make much difference. All the Head Start program children where ahead until about 3rd or 4th grade and then fell behind. Genetics does play a role. My sons went through a Christian School system which we really liked, and yes, it was a sacrifice for tuition, but it was worth it.