Whether you're looking forward to an empty nest or dread the day your child will leave to start their own life, it's likely to happen after high school. While their lessons in life certainly won't end in early adulthood, they need to be responsible and independent people when they get out on their own. It's up to you to make sure that they are taught ways to do just that before they leave high school.

Money Matters
The Washington Post argues that while most high schoolers will graduate with basic reading, writing, and mathematical skills necessary for adulthood, they don't learn nearly enough about money. Teach your kids about banking, income, spending, and tracking their money. Some of the biggest decisions they will have to make after high school will involve money, and even the small decisions they make dozens of times a day will center around finances.
Boarding School
Boarding schools are available across the nation, such as the Delphian School in Oregon. These can be effective institutions for educating your child about many things in life. While there is an emphasis on academic curriculum, students also stay in dormitory-style settings on campus. They might stay there all week long and return home on weekends, or they might be there seven days a week. In either case, they learn how to coexist with others but have some independence away from their family.

Time Management
Children have very structured lives as they go through the first two decades of life. When their schedule isn't dictated by classes and schooling, it's often up to you as their parent to decide what they do, where they go, and when they do anything. As adults, they might have bosses that dictate their work schedule, but they also might not if they wind up freelancing, doing remote work, or entering the gig economy. They need to know how to manage their time wisely in both structured circumstances and free time.
Even if your child is moving on to college or university after high school instead of living on their own immediately, they still need to know how to be independent and responsible individuals if they are going to be successful in their next stage of life. Time management and fiscal maturity are both things that they need to learn how to develop, and boarding school might be a place to help them find their own feet away from home.