an excerpt from the Texas Homeschool Coalition site says
....the only requirements for home schooling to be legal are that
(1) the instruction be bona fide (i.e. not a sham)
(2) the curriculum be in visual form (e.g. books, workbooks, video monitor)
and (3) the curriculum include the basic subjects of reading, spelling, grammar, mathematics, and good citizenship.
Parents may obtain curriculum materials from outside sources or develop their own. They may also send their children into the home of another parent for instruction or have a tutor come into the home for all or part of the instruction.