When they fell in love, she was barely into her teens, and he wasn't much older. Some saw a star-crossed couple who found understanding, joy and maturity in each other's arms. Others saw impulsive kids whose reckless passion cut them off from family, friends and more appropriate interests, provoked mood swings, delinquent behavior and experimentation with drugs, and ended in tragedy.

Romeo and Juliet's story is centuries old, but these two very different views of adolescent romance live on, often simultaneously, in the minds of bemused parents.

Lately, teenage romance has caught the attention of a number of researchers, who are increasingly interested in its potentially positive as well as negative effects -- not just on adolescence, but on adult relationships and well-being.

According to Dr. Wyndol Furman, an editor of the book ''The Development of Romantic Relationships in Adolescence,'' understanding teenage dating means understanding that adolescence is ''a roiling emotional caldron whose major fuel -- more than parents, peers or school and almost as much as those things combined -- is the opposite sex.''

Dr. Furman, a professor of psychology at the University of Denver, said adolescents' lack of social skills and emotional control can make relationships difficult. Yet, he said, romantic relationships can also be significant sources of support that offer teenagers fun and companionship, help them forge mature identities and offer them practice in managing emotions.

''Growing up involves risks,'' he said. ''Parents are naturally concerned about their teens' relationships, but they shouldn't want them to just stay home.''

Setting guidelines requires an appreciation of the profound differences between 13- and 19-year-olds. Among the so-called ''tweens'' of middle school, Dr. Furman said, the point of a crush ''is mostly to be able to say you have a boy- or girlfriend,'' and to start to know the opposite sex. Next, he said, boys and girls date in groups -- ''you kiss, then go to the movies'' -- and become more interested in the close companionship sought by older teenagers.

Teenagers' growing capacity for positive romantic relationships has been traced by Dr. Reed Larson, a professor of human and community development at the University of Illinois. After paging his teenage subjects at random times during the day and inquiring about their activities and emotions, Dr. Larson confirmed what parents since Adam and Eve have observed: adolescents are either very happy or very unhappy much more often than adults, especially concerning romance.

But Dr. Larson correlated their more numerous negative responses to what he called ''a certain randomness'' and superficiality in their attachments, which make their relationships less rewarding. Indeed, he said, this dissatisfaction is most pronounced among among the younger, less experienced teenagers, who ''haven't yet learned how to have fun and get along.''

He observed, ''It takes time for a teenager to realize that a relationship isn't just an infatuation based on haphazard attraction, but an entity on which two people with compatible personalities work together.''

Earlier studies of youthful romance tended to focus on its risks and those who were most vulnerable. A survey conducted by Dr. Jay Silverman, director of violence prevention programs at the Harvard School of Public Health, published in August in The Journal of the American Medical Association, reported that about one in five high school girls had been physically or sexually harmed by a dating partner -- about the same rate at which adult women report being abused by partners.