We did this 2 years ago. I called the school to request "early entrance to K". Because my son was so young, he was too young for the school's early entrance policy. (You can probably read your school's policy online or request a copy.) Because of this, he fell into the "whole grade acceleration" policy.
The school was very negative (bordering on rude) in my interactions with them. Because of their policy, he needed an IQ test, achievement test, and meeting of the "acceleration team". (The school provided all testing free of charge.) He couldn't be denied the testing because of the school's own policies, but he was the youngest child to ever go through it so they were very resistant. After the testing, their tune really changed, and they were so excited about him. The whole process took some time, so I would contact the school ASAP.
