Not all kids are cut out to go to public school. Some do much better when taught at home by a parent, older sibling, or even a hired home school teacher. Although obtaining your diploma had to be accomplished in a local high school back in the day, this is not longer the case.
Every state has its own laws regarding homeschooling so be sure to research the rules for your state.
With a computer and good online access, it is actually possible to take classes from an accredited high school online and get a diploma. Do a little research before getting started and most importantly, have a plan to stick to. Home schooling does require discipline. However, this might be the best way for your child to get an education and is certainly worth a try.