If your child is bored with high school topics, you can consider two choices: college options and non-college options.
College options include going to a university at an early age (either as a regular student or "Non-matriculated" student) or attending a community college before going to the university. College policies vary on non-matriculation. College like to get money, however, and usually non-matriculated students pay the full price (no scholarships). Since it's basically "free money" for the college, they are highly motivated to accept those students. With these options, the student is in a classroom with college-age people on a daily basis.
Non-college options include homeschooling college and other distance learning opportunities, where most of the academic work is done at home, similar to homeschooling. View this quick video on the process:
Also check out my Dig Deeper page on homeschooling college:
These are the books I recommend on the subject:
"Accelerated Distance Learning" by Homeschool Graduate Brad Voeller.
or Bears Guide To Earning Degrees By Distance Learning
Here's how it works: You pick and choose from online classes across the nation. All the work is done at home. All the results from those different online experiences are all sent to one university. If you choose to do it all four years of college this way, some (but not all) of the upper level courses require you to fly to the distance location for testing once a quarter. That University will provide "accreditation" for all the credits that are earned. Those accredited transcripts will be sent the next University your student wishes to attend. It's possible to homeschool college from one quarter to all four years.
Looking for a college? Try my Teachable Moments DVD, "Finding a College"