Here's the information for FCPS:
http://www.fcps.edu/dss/osp/StudentRegistration/homeinstruction/
If you live in VA and your child is five, they are required to attend school. I think this is the correct statute:
Section 22.1-254 of the Code (the compulsory attendance law) provides:
Except as otherwise provided in this article, every parent, guardian, or other person in the Commonwealth having control or charge of any child who will have reached the fifth birthday on or before September 30 of any school year and who has not passed the eighteenth birthday shall, during the period of each year the public schools are in session and for the same number of days and hours per day as the public schools, send such child to a public school or to a private, denominational, or parochial school or have such child taught by a tutor or teacher of qualifications prescribed by the Board of Education and approved by the division superintendent, or provide for home instruction of such child as described in § 22.1-254.1….