The end of summer vacation is in sight. You know what that means: time to go back to school. It means new clothes, new notebooks, new teachers and new friends. And it means homework.

During the school year, kids have a lot to do. After-school sports, music lessons and doing things with friends and family all take up time. Then there's that history assignment to finish and the math problems to solve and the spelling words to memorize. Sometimes, it feels like there's no time left just to do nothing.

Even though there are so many demands on kids' time during the school year, they do manage to squeeze in lots and lots of hours of one particular activity, experts say. That activity can get in the way of your homework, your friendships, your time with your family. And it can keep you from getting the exercise you need.

What is it? Watching TV.

Studies have shown that kids who are successful in school watch less TV than kids who do poorly. You don't have to be Einstein to figure out why. It's hard to get your homework done or to get enough sleep if you're up until 11 every night watching cop shows.

In addition, many experts worry that seeing all the violence that's shown on TV can disturb young children. It can make them more aggressive than they might be otherwise. It can make them think that fighting or using force is an acceptable way to solve problems.

Educators worry because many kids spend as much time watching TV as they do in school. In 1987, a fourth-grade teacher in Hutchinson, Minn., decided to do something about it. Pat Marker had heard about a boy in New Jersey who went for one whole year without watching any TV at all. Marker didn't expect the kids he taught to do that, but he challenged his students to turn off the tube for 30 school nights. Nineteen kids did it. Marker called them the "TV Busters" and held a party for them.

From there, Marker's idea grew. The next year, 101 kids became "TV Busters." In 1989, more than 750 kids in several different elementary schools took part in the program. In 1990, Marker expects even more kids in Minnesota schools to become "Busters." If you're a Buster, you don't have to give up TV altogether. But you agree to keep the set turned off on school nights (Monday through Thursday) for 20 nights.

There are exceptions: You can watch the Discovery channel, the news or public television -- but you have to have your parents' permission to watch those shows. On weekends, you can watch anything you want to. TV Busters fill out daily slips reporting on what they do each night. Parents have to sign the slips each night. At the end of the five-week program, kids earn prizes.

Marker says his mission is not to wipe out TV watching entirely. But he wants to get rid of unnecessary TV watching. He'd like kids to become TV viewers who choose to watch, not just viewers who turn on the set and stare at whatever's there.

Without TV, what are you supposed to do at night? Marker has some suggestions:

Read a book.

Talk to your parents.

Read the newspaper.

Listen to the radio.

Think.

Play with friends.

Try a new recipe.

Draw a picture.

You can probably think of other non-television projects yourself. Studies have shown that when families limit TV time, good things happen. Kids spend more time with the adults in the family -- and do more helping out around the house. Kids read more, play more imaginative games, spend more time outdoors and get more exercise.

What are your family rules for TV watching? Do you limit the number of hours the TV is turned on? Do you read the TV listings and make choices about what to watch and what to skip? The Center for Media and Values in Los Angeles suggests that families plan TV program selections in advance each week. The center also advises parents to watch TV with their kids -- and to talk over what they see.

Television isn't all bad, of course. There are lots of great shows. By watching TV, you can find out what's going on in the world. You can learn about science, nature and art. A good TV show can make you cry or laugh. And watching TV can be an activity that families share.

The trick is to make sure you control the TV -- not the other way around.

Tips for Parents

For more information about Minnesota elementary schoolteacher Pat Marker's "TV Buster" program, you can write to him at Park Elementary School, 100 Glen St. S., Hutchinson, Minn. 55350. Teachers can order a starter kit containing a description of the program by sending $2 to cover postage and handling. Worried that your kids will whine, "There's nothing to do," when you turn off the tube? Arm yourself with "The Kidfun Activity Book" by Sharla Feldscher and Susan Lieberman (Harper & Row; $6.95). The book lists 250 easy activities for kids ages 2 1/2 to 8. All of the projects can be done with stuff you have around the house.

Catherine O'Neill is a free-lance children's writer.