J.J.
Hi,
I too have a 4 yo with a summer birthday and have decided to either keep her home next year and teach her myself or send her to pre-k for another year. In Pa kids do not have to start school until age 8, so even if I send my daughter to pre-k next year, I can start her in 1st grade the following year. Kindergarten, 1st and 2nd grade are not mandatory, but the child will be tested as all potential school students are, even kindergartners, and they need to meet certain criteria(IT is really easy to meet IMO). So you can keep him in pre-k next year and then decide if you want to send him to kindergarten or 1st grade the following year. But realizing that you could send him to first grade when he is 6 and if you feel he is ready may help you be more at peace with keeping him in pre-k one more year.