Parents play an important role in determining how teenagers adjust to their emerging sexuality. Many mothers and fathers, however, are caught off guard when their innocent-seeming youngsters start to look and act grown up. As a result, they may miss their opportunity to exert a positive influence. If you're the parent of a teenager, your challenge is to come to terms with your child's sexual maturation, show your trust and give advice.

Most children learn something about sex, family life and sexually transmitted diseases at school. No matter how good the curriculum, though, your teenager might not hear everything he or she needs to know. That's where parents come in. Awkward as it may be, you need to reinforce and supplement what gets covered in school. And you certainly can't rely on school to foster your teenager's self-reliance and clarify his or her values. Those attributes develop only over time and with parental guidance. If you're not sure how to get started, ask your doctor or other trusted individuals to suggest helpful books for both you and your teen.

In the idealized past, a sober talk with a wise and sensitive parent could set a youngster on the proper path for life. Today, though, sex is a staple of news, entertainment and advertising. You'd think it would be hard to avoid this ever-present topic — but when parents and children need to talk, it isn't always so easy.

"If you wait until 'just the right time,' you'll miss the best opportunities, " says Robert V. Johnson, M.D., a pediatrician at Mayo Clinic, Rochester, Minn. "Don't think in terms of having a single birds and the bees talk with your child — they need your guidance in many ways over the years. Events as commonplace as reading an item in the news or viewing a TV show or movie can serve as a comfortable way to ask your child's views and to share your mature guidance."

Leave the way open for additional discussions. Sometimes good topics can come up at inconvenient times. It's okay to say something like, "That's an important concern, I'd like us to talk more about this when we can give it the time it deserves." For many families, a long car ride with just the parent and child is a great time for relaxed, open-ended discussion. Sometimes a shared after-school or late-night snack is a good opportunity.

Don't worry if you feel uncomfortable at first. Discussing sex with your teenager may be easier if you start by talking to your partner or a close friend about your goals and concerns. You can compare each other's impressions about your child's sophistication and understanding or even rehearse discussions of difficult topics. This preparation may help you find the right words when you sit down with your child.

A possible icebreaker is to ask your children for comments about their peers — have them explain the atmosphere at school among their classmates concerning sexual behavior. Teenagers may be more likely to open up about themselves or their closest friends after they've had a chance to gauge your reaction to more general information about what the other kids in school say and do. You're not out to get confidential information about your child's classmates; your focus is on learning more about today's teenage world, which is probably much different from the world you recall.

During your discussions, be honest and own up to your discomfort, explaining why you think it's important for your teenager to get information about sexual matters from you. He or she may respond to your conversational overtures with silence. Say what you have to say anyway — your teen will hear it, and it will likely help. Don't feel that in order to promote discussions you need to tell your teen a permissive message — teens respect your honesty, even if you tell them they're still too young for sexual intimacy.

Sex education is most effective if you make it an ongoing discussion, beginning in the preschool and school-age years. Well before your child begins sexual activity, he or she needs your support and assistance in understanding sexual feelings, defining sexual behavior and learning to respect him- or herself and others. Give honest, straightforward answers when your child asks questions about sex. If he or she never asks questions, don't assume that the silence is due to lack of interest. Bring up the subject when the opportunity presents itself.

Topics that may arise during the teenage years include:

• Dating. Some questions your teenager may have are: "When can I start dating?" "How will I know when I'm ready to have sex?" "Won't having sex help me keep my boyfriend or girlfriend?"
• Abstinence. A number of factors — peer pressure, curiosity and loneliness, to name a few — steer teenagers into early sexual activity. Tell your teenager that many young people avoid sexual intimacy until they're definitely ready for it. Couples can express affection in a number of ways without having intercourse. They can enjoy intimate talks, long walks, holding hands, listening to music, dancing, kissing, touching and hugging.
• Date rape. Explain that no one should engage in sex — even with a boy- or girlfriend — out of a sense of obligation or fear. Any form of forced sex is rape, whether the perpetrator is a stranger or someone your child has been dating. Impress upon your child that no always means no. Also emphasize that alcohol and drugs impair judgment and reduce inhibitions, leading to situations in which date rape is more likely to occur. In addition, warn your teen about date-rape drugs.

• Heterosexuality, homosexuality and bisexuality. Many young people wonder at some point whether they're gay or bisexual. Help your child understand that youngsters who aren't gay or bisexual do sometimes have crushes on members of the same sex. Make it apparent that if your teen is gay or bisexual, you won't reject him or her.

Don't rely on scare tactics to discourage your child from becoming sexually active. A purely negative approach may stop him or her from asking important questions and cut you off as a future source of information. Also, threats and warnings are less effective in discouraging unwise sexual activity than are calm and reasoned discussions of the risks. Gather your facts and present them objectively, then examine questions of ethics and responsibility in the context of your family's system of beliefs.

The same holds true for teaching youngsters about drug and alcohol abuse, which may accompany sexual experimentation. Gear your messages about alcohol and drugs to your adolescent's level of intellectual and moral development. Particularly in early and middle adolescence, your child may be less impressed by the long-term health risks of these substances than by their immediate social consequences. Even more important than delivering an anti-substance abuse message is to set a good example through your own lifestyle. Be a role model.

If you're like most parents, you want your child to delay the start of sexual activity until he or she can behave responsibly and ethically. Unfortunately, many teenagers become sexually active sooner. What can you do?

Keep the lines of communication open. Make your feelings known, then set and enforce reasonable boundaries — curfews and rules about visits from friends of the opposite sex, for instance. In that way, you can avoid power struggles. Explain your objections thoroughly, whether they arise from religion, concern about your child's well-being or a combination of the two. Also talk about the possible consequences of early sexual activity, from emotional pain to infection to unplanned pregnancy.

Even if you've had repeated informative discussions about contraception and sexually transmitted diseases, it's worthwhile to go over that territory again. Stress the importance of keeping a sexual relationship exclusive, not only as a matter of trust and respect but also as a means of risk reduction. The more sexual contacts your partner has had, the greater your risk of contracting a sexually transmitted disease from him or her.

Identify additional sources of information and support for your child. During the adolescent years, allow time for your child to have a conversation with his or her physician in a supportive and confidential atmosphere to address sexual activity and other behaviors.

"Sexuality is a wonderful aspect of many adult relationships," says Dr. Johnson. "Most parents want their children to develop healthy sexuality as they mature. Sexuality as portrayed in the media may involve casual relationships, unusual sexual acts and even violence. Children should know that, especially in a monogamous, long-term relationship, sexual relations are a beautiful expression of mutual love and trust. Despite what the media suggest, sexual behaviors don't need to be learned and experienced before marriage or a long-term relationship."