"You know what to do if you're caught in a rip current, right?" I ask anxiously, wanting to impart this last bit of knowledge to my son before he leaves us — and his childhood — behind.

We sat on a beach in the Florida Keys, a last family vacation before he headed off to college, joining a projected 18 million students at campuses this fall. My riptide worries, a metaphor for my jitters over that life-changing milestone, provoked a sigh.

"Yeah," he said wearily. "You tell me every time we come here."

Doubts over how well we've prepared a child for life's tough currents are a common affliction of parents sending a student off to college. Just as common is the advice aimed our way: Let go.

It's a message colleges stress — every chance they get. The dreaded "helicopter" parent who drops in to fix problems is the focus of orientation workshops. Topping schools' recommended reading for parents are books about letting go, prominently displayed in campus bookstores on move-in and orientation days.

At a time when parents are proud and thrilled their child is taking this big step, they're told to step back. The thrill is tempered by sadness. Their job — a big part of it, anyhow — is over.

"It's a loss. It's the end of the chapter of your life with that child. ... You don't get any more do-overs," said Dr. Andrea VanSteenhouse, a psychologist and author of "Empty Nest ... Full Heart: The Journey from Home to College" (Simpler Life Press, 2002), a book high on colleges' suggested reading lists.

Besides loss, there's worry. When children live elsewhere, parents don't know what they're doing or even whether they're OK. College is no safe haven, as the murders at Virginia Tech last year illustrate. Worries about date rape, assault, hazing, drinking, drugs and other perils can keep moms and dads up at night. Schools try to create a safe environment, but their efforts can't match a parent's vigilance.

Privacy laws, in fact, can prevent parents from seeing their child's grades or knowing about problems — including medical ones — without the student's consent.

Colleges see that as a good thing.

"Parents really do have their children's best interests at heart but sometimes, out of the desire to be helpful, get in the way of their child becoming independent," said Karen Levin Coburn, associate dean for freshman transition at Washington University in St. Louis and author of "Letting Go: A Parents' Guide to Understanding the College Years" (HarperCollins, 2003).

Like many schools, James Madison University, in Harrisonburg, Va., where my son is attending, warns parents not to "helicopter" in to fix problems because it robs students of the chance to learn problem-solving skills. In summer orientation for freshman parents, students acted out a wickedly funny skit of a parent weeping after moving a student into the dorm. In another skit, a "parent" donned a helmet and grabbed a sturdy rope to drop to her student's rescue in superhero fashion.

Parents know they can't teach children all they need to cope with whatever college — or life — throws their way. They know they must give children freedom to become adults. But it's not easy.

"Some feel an emptiness when they realize just how much that child filled up their lives," said VanSteenhouse.

Sending a child off into the world gives parents the opportunity to re-evaluate their marriage, friendships and other relationships — which experts say is a good thing. Change, they note, is part of growth.

"If your child has been your 'couple life,' it's the time to wake up and look at that person and you hopefully have something to reconnect to," VanSteenhouse said.

"It's a time when the relationship has a chance to breathe a little ... for some people that's good and for some people that's scary," said Dr. Carole T. Goldberg, psychologist at Yale University's Mental Health and Counseling Center.

Children still at home can benefit from the new family structure. "As much as everybody notices the hole in the fabric, it can be a very special time for the ones who have been waiting to step into the forefront and claim their space," VanSteenhouse said.

But how to take your focus off the loss of your student? Should you take up watercolors, surfing, a foreign language?

"You get to choose where you want to spend your energy," VanSteenhouse said. "(But) I like it when people take a little time to adjust. ... Lower your expectations about how quickly you're supposed to pull this together."

Friends can help, but if the main thing you had in common was children, those friendships may no longer work so well. It may be time to form new friendships or reconnect with those set aside in the child-rearing juggernaut.

As for that dreaded goodbye at the dorm, try to keep things light. If you can't get through it without crying, "it's certainly not destructive to have them know it's hard for you, but I think it is a sign it's time to leave," VanSteenhouse said.

When children are happy at college, parents relax and begin to enjoy the freedom of cheering from the sidelines as students navigate their own course. And while moving away changes day-to-day interaction, it doesn't alter the basic parent-child relationship, Goldberg said.

"Children will always need their parents, and parents will always need their children," she said. Separation leads to the next stage, that of "being adults together."

"If you do a good job, they'll grow up and leave you but return as an adult," Goldberg said.

MORE COPING TIPS

Parents sending a child off to college for the first time?

• Be prepared to go through a period of reevaluation of your marriage, friendships, and relationships with children still at home.

• Give yourself time to adjust. Accept that it won't happen overnight and may be painful.

• Take up activities and interests that seem fulfilling, but don't try to come up with "busy work" to fill the void. This is a time for developing, refocusing and growing.

• Keep it light. If you cry when dropping your child off at college, also try to laugh at yourself a bit. Don't lay the burden of your unhappiness and anxieties on your child.

• Avoid offering last-minute advice on everything you think you didn't cover sufficiently. Your child is preoccupied with the coming adventure and isn't listening.

• Resist the temptation to rush to fix your student's problems. Parachuting in robs children of the chance to develop problem-solving skills all adults need.

• Don't call your student all the time just because both of you have cell phones. Think about setting aside a regular time for communication.

• Don't orchestrate a massive family gathering on your child's first big holiday home without first talking with your student. He or she may have other ideas.

• Don't take it personally if your student prefers to spend "home time" with friends, instead of you, especially the first year.

• Realize that while your caretaking job as a parent is done, a new and maturing relationship with your child is forming that can hold deep satisfaction for both of you.

• Remember that even when your children live elsewhere, your spot in their heart is permanent.

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College kids leave nest empty.