Does anyone know the procedure? This is for Kindergarten, which is not mandatory in my state.
If you're not upset with the school, maybe you could just ask the principal.
In my state, we have to submit an "intent to homeschool" letter to the superintendent with a little bit of info about our plan.
You should be able to find out exactly what to do at the HSLD website.
However, if K is not mandatory, you should probably just go to the office and ask how you can "un-enroll (?)" your child.
This probably depends on the state, but I've heard that once you're in the system, you're in the system... so even if K isn't mandatory you might have to go through the same hoops as for an older student.
In WA state, you don't have to file intent to HS before 8 years old. If you were to pull the child out, you would just write a letter to the principal stating you will be bringing the child home. I'll file an intent next year when he's 7, but I did not this year at 6 in 1st grade.
Here's a link to the homeschool laws for WI. http://dpi.wi.gov/sms/homeb.html
There's a form that you fill out online at the link above (very simple-- you don't even have to list your children's names), and once the DPI has received it (which should be essentially immediately after you send it in), you can start homeschooling.
Here's a link to the Wisconsin Parents Association's website that answers your question: http://homeschooling-wpa.org/faq/#soon