Homeschooling is legal in all fifty states and the District of Columbia. Here you can find the requirements you need direct from your state’s official government site. You do not need to join any organizations or even spend a dollar to begin.
District of Columbia
N.J.S.A. 18A:38-25 requires that “every parent, guardian or other person having custody and control of a child between six and 16 to ensure that such child regularly attends the public schools of the district or a day school in which there is given instruction equivalent to that provided in the public schools for children of similar grades and attainments or to receive equivalent instruction elsewhere than at school.”