Yes, we did just that. My story is all over this board (I've been here awhile!) but would be glad to answer questions.
We had to work hard to get the early entrance to first and don't regret it for a moment. In fact, the one skip wasn't enough as he is now subject accelerated in math. DS is now almost 8 and in third grade.
We started by attending the K registration and then requesting a meeting to discuss needs based on some private testing we'd had completed. We ended up having to take him for more testing and waiting until just two weeks before school when they finally agreed to place him in first grade. In IL K is not mandatory, the law just says that a child has to be 5 to enter school and that accleration is up to the individual district.
