CHICAGO — When Brenda Lee was a teen in the 1970s, she had one — and only one — best friend throughout high school.

So, Lee worried when her 15-year-old daughter, Robyn, seemed to be cycling through a new best friend every six months at York Community High School in Elmhurst, Ill.

"It's like a bad thing to have one friend," explained Robyn, who clarified that she actually has four best friends at all times, with 15 to 20 other close friends she considers part of her regular social circle.

"If you have one friend, it means only one person likes you," she said. "That's not cool."

Technology, modern-day parenting techniques and societal norms have made it possible — if not preferable — for teens to claim hundreds of friends on their Facebook pages, to text weekend plans to dozens at a time from their cell phones, and to spend hours electronically keeping up with people they barely know rather than actually talking to one close friend.

For decades, experts studying teen cliques have known that teenagers prefer to travel in packs. In studies conducted in 1963 and in 1995, researchers found teen friendship groups averaged six persons, said Melissa Witkow, an assistant professor of psychology at Willamette University in Oregon.

In 2005, when teens were asked to estimate how many friends they kept in touch with regularly, the average answer was 20, according to data from the Pew Internet & American Life Project.

"When I think of myself growing up, you lived in your neighborhood and you had your best friend that lived down the street from you. You didn't necessarily travel in this powerful pack," said Susan Bartell, a New-York based psychologist who specializes in teens and tweens. "Now the group is where they're getting their strength from."

The shift to group-style friendships has notable upsides, such as increasing the likelihood of more diverse connections and boosting teens' self-esteem by giving them a place to belong. A study published last summer in the online edition of Journal of Research on Adolescence showed that teens with more friends in school had higher grade-point averages.

But those monitoring the change also are paying attention to potential downsides.

"The notion of friendship is still critical, but it's becoming much more complicated," said Bernardo Carducci, a professor of psychology at Indiana University Southeast.

In a sample collected last week from 70,000 Facebook pages, 10- to 20-year-old users had a median number of 440 friends. That's more than double the 197 median for those 40 to 50 years old, said Dan Zarella, who gives marketing lectures about how to understand such trends for HubSpot, his company, based in Cambridge, Mass.

MaryRose Moss, a 17-year-old in Chicago, knows firsthand how friendships can accumulate. She created a Facebook page when she was 14 and within months counted, among her group of 500 friends, teens she hadn't seen since kindergarten and others she had met only once. The high-school senior eventually got rid of her Facebook page because just reading her friends' news updates could take an hour.

Text messaging has opened the door to many new connections, she said.

"I'm friends with some people that I wouldn't be as close to if it weren't for technology," said Moss. "It's so easy to send a text to somebody even if you didn't know them very well."

Her parents marvel at the ease in which their daughter collects friendships and at the way she and her friends hang out in big numbers, even on first dates or while attending a school dance.

Many of today's teens grew up with their parents managing their free time, from arranging play dates to enrolling them in organized sports and other activities. Some psychologists wonder whether, now, social-networking technology is further delaying opportunities to learn negotiation and other socializing skills children once derived from making friends the old-fashioned way.

"If somebody disagrees with you, you can 'defriend' them with the click of a keystroke," said Carducci. "You don't get that practice, you don't get that connection, you don't get used to having to do the work."

Bartell, a psychologist and author of The Top 50 Questions Kids Ask, said she has seen some teens identify with a group so closely that they give their groups names or label members of the group siblings on Facebook.

But the same group that makes some teens feel part of something can make teens on the outskirts feel even more alienated, Bartell noted.

Marianne Boe, a social-studies teacher at Resurrection High School in Chicago, sees signs of changing friendship in the hallways. A decade ago, she could easily identify clusters of girls who stayed friends through all four years of high school. Today, it's harder to pinpoint the cliques because they are more fluid, Boe said.

"They've got all these friends, but they don't have those intimate ties," said Boe. "It's easy to convince yourself you have a million friends, when really, who are the ones who know dad is out of a job? Or who know that your parents are getting a divorce?"

Other research suggests that teens' friendship habits today are different but not detrimental.

Studies show that the groups teens associate with most closely online are still friends made at school and through extracurricular activities. The Internet often enhances those relationships, said Vili Lehdonvirta, of the Helsinki Institute of Information Technology.

"It's just a continuation of existing friendships," said Lehdonvirta, "a way of overcoming issues of distances."