In the first few days of school, you probably get home feeling pretty worn out. It's exhausting to exercise your brain after vacation -- and your body gets tired, too. But if you think you're tired, you should try being a teacher.

During the first week of school, teachers go home with hoarse voices and sore feet. After all, the poor things have been standing up all day long. "My feet are killing me," they complain.

You probably don't spend a lot of time thinking about your feet, except when you're deciding what kind of shoes to put on them. But feet carry your body wherever you want to go. You run on them and jump on them. They balance and support your entire body. They let you stand on tiptoe, hop, leap, skip, walk backward and dance.

Feet are pretty remarkable -- a complex arrangement of 28 bones and 19 muscles. They're movable because 35 joints in each foot allow you to change the position of the bones. Flexible bands of tissue stretched between the bones hold all this complicated machinery together. These bands are called ligaments, and there are 100 of them in each foot.

The muscles in your feet aren't quite as complicated as the ones that make your hands work. But they work in a similar fashion. Feet, like hands, are flexible and can be used to grasp things. You can probably hold a pencil with your toes and even write your name with it. But you'd have a hard time doing your homework that way, and it would be pretty messy. You don't have the delicate control of your foot muscles that you do of your hand muscles.

Your feet are designed to keep you standing upright and to help you move forward. Your big toe helps you walk. Each time you take a step, you use it to push off. That toe has a bigger, thicker bone than the other toes. Your useless-looking baby toe helps you keep your balance as you walk.

Ever wonder why the skin on the bottom of your feet doesn't wear off the way the soles of your shoes do after a while? It's designed to stand up to a lot of use. The skin on the bottom of your feet is thicker than the skin on the rest of your body. It's a good thing it is; foot doctors estimate that kids take between 7,000 and 8,000 steps every day.

The complex structure of your feet can cause trouble. Doctors report that foot problems are one of the three most common health complaints, along with colds and tooth decay. You can take care of your feet -- and help avoid problems -- by using these foot-care tips.

Wash and dry your feet thoroughly every day. Be especially careful to dry between your toes. Germs thrive on dampness.

Cut your toenails straight across. Rounded toenails can become ingrown and get infected, which really hurts.

Never pop or tear a blister.

Wear shoes that fit. If your shoes feel too tight, even if they're your favorite shoes in the world, get rid of them. Kids' feet continue to develop well into the teenage years. They need room to grow.

Change your socks after a workout to avoid dreaded sneaker smell.

Never borrow someone else's shoes. You could catch an itchy fungus called athlete's foot.

Above all, be kind to your feet. After all, they hold you up. Tips for Parents

What should parents know about buying kids shoes? A booklet, "Caring for Your Children's Feet" published by the National Youth Sports Coaches Association reports that kids' feet keep developing from birth until well into adolescence, until about age 14 to 16 for girls and 15 to 21 for boys. During periods of rapid growth, kids may need new shoes as often as every three months. When you buy new shoes, make sure that there is sufficient room in the toe box (the area between the upper and lower portion of the shoe). A good rule of thumb: There should be a space the width of your thumb between the child's toe and tip of his shoe. Here's news that should be a relief. The booklet, which was written by orthopedic surgeons, says that well-cushioned, pliable athletic or gym shoes offer sufficient support for growing feet. So you don't need to try to force your kids into sturdy oxfords this fall. For a free copy of the booklet, write to "Caring for Your Children's Feet," Suite 1214-HK, 303 E. Wacker Dr., Chicago, Ill. 60601.

Catherine O'Neill is a freelance children's writer.