There are as many answers to this questions as there are families who homeschool. Some homeschool for educational reasons, some for religious reasons, others becuse they like to be together as a family. Some families who are challenged by living with a child with a physical or emotional problem find homeschooling to be easier and more consistent than public schooling. While the vast majority of homeschoolers come from white, two-parent, Christian families, this is not the only model.
Single parents are able to homeschool as well as lower, middle and upper class families.
Homeschooling is legal in all 50 states in the U.S. as well as in Canada, the U.K., Australia, France, New Zealand, and elsewhere. However, each place has a different law. Write to your State or Province Department of Education or check a law library's Statute Book for exact wording. In some areas you register with the state, others with your local school or school district. Some areas require you to submit a plan of study and have your child be evaluated each year by testing, teacher evaluation, portfolio or other method.