I second the "what your X grader needs to know" series. It's a good place to start from. Also you can look up your state educational standards and just make sure you cover them in some way or another.
When the kid knows more than the teacher? I think that happens a lot in school to HG kids. I think Wolf knows more than I do about dinosaurs and possibly the solar system. The answer? Books, books, and more books with a side of internet thrown in for good measure. Then you can add in mentors or outside classes etc...
Also if your district offers a homeschool based charter or Independent Study program you could see about transferring to that. It will give you the teacher back up and support you might feel you need starting out homeschooling (it's what I did) but you still have to make sure it's a good fit... Also most curriculum supplies are supplied by the district that way and you can still work at your own speed and level.
