School isn't for everyone. Many intelligent teens hate school because they're bored or face social problems such as bullying. Unfortunately, an education is often the key to a successful future, so completely giving up on school is rarely a sound option. If your teen dreads getting up every morning, it's time to start looking at alternatives. She can continue her education without sacrificing her sanity.
Research other schools in your area. Your child may find that he's happier at a public school or a parochial school. If you live in a relatively urban area, you might even have special-interest high schools, such as schools that focus on the arts or sciences in addition to the typical high school curriculum. A student who tests as gifted could benefit from a school that caters to the needs of gifted students. Any of these could be just the change your teen needs to respark his interest.
Plenty of families find that home schooling offers the flexibility they need to thrive. One option is to join an online public school, which follows the traditional curriculum, but is all done online from home. Other options include buying other prepackaged curriculum or simple "unschooling" by letting your teen follow her interests. Research your state's laws regarding homeschooling because laws vary widely.
The typical high school curriculum leaves open space for study halls and elective courses in addition to the required courses. Some schools will allow a bright student to graduate early by taking accelerated classes. For example, if your teen doubles up on English and social studies classes, he might be able to meet all the required graduation classes in three years. Because he'll have a difficult course load, he'll have to focus on his studies, leaving less time to focus on hating school. Then, he'll have the high school diploma and can move on with his life.
If the classes your teen is taking in high school just aren't challenging enough, find out whether she can take courses at a nearby college. Many high schools allow students to take high school classes in the morning, then take a bus to community college. In some cases, the college courses will count toward their college degree after high school, but even if they don't, your teen will still be happier with more challenging material.