Kindergarten enrollment varies across states, school districts and schools. I suggest contacting the school district for your residence to inquire about their kindergarten enrollment policies and procedures. You may use SchoolFinder to research the phone number for the school districts in your area: http://www.education.com/schoolfinder
You can also visit the website for your state's Department of Education to research state law (and academic standards) with regards to kindergarten.
I'm including some additional resources below you may also find helpful in preparing for this special milestone in your child's education. Thank you for asking!