Some districts do allow transfers to other schools within the district if the parent does not want their child to attend the assigned school. Contact your local school district to learn more about their transfer policies, and to discuss any concerns you have about the school to which your child was assigned. You can use SchoolFinder to research the contact information for U.S. school districts (and schools): http://www.education.com/schoolfinder
Another option to consider is online school. There are public and private online schools, and you can learn more about this option on the SchoolFinder page linked above.
Below are some additional resources you may also find helpful for preparing for this special milestone in your son's education. Congratulations, and don't forget your tissue on the first day of school!
It may be worth finding out if the U.S. has an appeal system like over here in the UK. In the UK when parents choose schools for their children they put down 3 schools 1st choice, 2nd and 3rd. Most parents get 1 of the 3 schools on their choices form and that way their child attends a school they want, However, if I was a parent and I didn't get my 1st choice of school - (the local Catholic Primary school) I would appeal!. Parents can appeal to get their child into one of their preferred schools and most are successful in this appeal. So find out if you can appeal and then take it from their, as a parent it is your right to send your son to the best school possible and your choice of school.