I think it completely depends on the school, school district and state. If he is going into an age-appropriate grade, you will likely encounter very few issues. Grade-skips/acceleration (within the school) may require significantly more data to prove eligibility on your behalf.
For ours, we are homeschooling K for a 4.5 year old. We are doing a very "eclectic mix of curriculums" most being around the 1st-2nd grade level. Our hope for next year is to have DS enter a self-contained 1st grade gifted classroom at 5.5 years old (+1 acceleration in our state).
Our school is willing to consider this as long as we provide achievement testing (at our expense) indicating his academic level is appropriate for that grade. Our state does not require any standardized testing for HS kids at any age.
VPS will add a little more credibility to your teaching endeavors (especially for an older child) but don't offer the flexibility of customization that you can create with other curriculum choices.
