Men are like dogs, whose social groups are marked by dominance hierarchies that lock into place fairly early after sniffing each other out, and where the many members largely accept their place in the pecking order. Girls, though, are like cats and give a contemptuous up-and-down examination to any new girl who tries to move in on her turf. Their social groups remain small because girls don't accept dominance as readily as guys do, and equality is harder to maintain as there are more people in the group.
Thus, male groups are pretty stable because with such a high level of inequality among the members -- from the top dogs to the underlings -- it would be stupid for any guy to try to climb the ladder. After all, you're already above the guys who you can easily defeat, and there are only a few people near your own level who you could displace. Going after the top rank is mostly impossible since that's too easy of a fight for the current leader. Of course, periodically one of the lower-ranking members may go through a growth spurt and join a few varsity sports teams, or discover their talent at the guitar and become famous in their high school, giving them a boost in status that lets them harmlessly ascend the hierarchy. Mostly, though, there is little point in conflict because the cases where it would make a real difference in ascending ranks will be so unevenly matched that the lower-ranking guy will not bother.
By contrast, because there are not that many members in a female group, even moving up one or two ranks could transform a sidekick girl into a queen bee. And because their group members are more similar status-wise -- less hierarchy -- girls will be often tempted to stage such a coup, given how evenly matched the contest would be most of the time: i mean i'm not gonna lie, i like her as a friend and all, but she needs to know her place and i could like totally take that bitch on. It's odd that Machiavelli isn't more widely read by teenage girls, given how the logic of realpolitik pushes against them all day every day, while law and order generally prevail among male groups in modern societies.
Much of this status-jockeying consists of fiercely monitoring the other girls' behavior and reporting the slightest infractions of one girl to the others, at which point the group more or less pins the offending girl down on the ground and all together leans on her chest to make her say she's sorry and it won't happen again. But often that won't be enough, and the girl will simply be ostracized and expelled from the group entirely. Moreover, because girls would rather not waste all the time and effort to monitor and perhaps eventually expel bad apples, they are much more ruthlessly discriminating right at the moment that a new girl expresses an interest in joining. (Guys aren't so choosy -- they'll find a spot for the new guy somewhere along the totem pole.)
On what basis would girls slam the locks shut on their clubhouse before the newcomer even made it to knock on the door? Anything that suggests she would be more dominant than the existing members and would immediately assume the lead role: i meannnnn who died and made THIS bitch queen? Behavioral clues might give such a girl away after close and lengthy inspection, but physical traits are easier to see quickly and from a distance. Clearly the one that matters most is sheer body size, primarily height but perhaps also muscularity. We therefore expect tall girls to be barred from most female groups, and as a result that they'll form their own tall girl groups where the female norm of mostly-equals will be satisfied.
The sociology literature shows that members of social networks tend to resemble each other in all sorts of ways -- males tend to hang out with other males, wealthy people with other wealthy people, sports fans with other sports fans, etc. Indeed, this is true for height as well (google "homophily height").
Still, from personal experience, it doesn't look so much like short girls hang out with each other, average-height girls with each other, and tall girls with each other. Instead it looks like tall girls have their own groups but that girls of below-tall height are OK making groups together. And to me it's most pronounced among the crowd at '80s night, where most of them are 18 to 21 years old and where the setting is a dance club. Competition over mates is most intense during adolescence and young adulthood, and when the environment is a lek rather than classroom, so we'd expect female groups to be especially likely to kick out tall girls in that situation. That's why we see a greater prevalence of tall girl outcast cliques in young dance clubs than in middle-aged office spaces or elderly retirement homes.
As an aside, I find that the tall girl clique is the best set-up if you want to approach one or bait one into approaching you. If the group is mixed-height and you approach the tall one, she'll already be nervous that you're singling her out for her height, but because no one else in her clique is tall, she'll feel extra peer pressure not to go along with it -- i mean i don't wanna be that person and hog the attention just because my legs are longer than theirs. But if all the girls are tall, none of them will feel paralyzed by that peer pressure.
And if you're not as tall as they are, you have to overcome their initial preference for taller guys. If you look at most famous cases of guys who have tall trophy wives, the guy usually belongs to the bad boy group that Alias Clio calls "mavericks", or high-energy go-getters who tend to fly solo and enjoy displaying their excellence through performance. Mick Jagger, Prince, and Tom Cruise come to mind. In a night club setting, the easiest way to show this is to give a more athletic performance on the dance floor: it shows that you're in shape and coordinated, but more importantly that you have a lot more energy or stamina and that you're a natural performer. I don't know why, but the tall girls who approach me in dance clubs are far more likely to spontaneously remark on how much energy I have, compared to what other girls say (e.g., omigod you have so much energyyy!!! vs. omigod you're such a good dancerrr!!!).
Perhaps tall girls feel a certain affinity with the maverick because both tend not fit into groups so well -- the latter because they don't want to in the first place, the former because their attempts to join groups usually result in getting locked out or expulsion. Both are more independent spirits.
Tall girls aren't really my thing (not that I dislike them either) because tiny girls ooze femininity more, but if they are for you, it's worth understanding where they come from socially and psychologically. Plus anyone who loves studying and portraying the variety that human beings come in (especially the unusual examples) should focus more on the Tall Girl, who tends to only get attention in popular culture as a one-dimensional femme fatale or butt-kicking babe. There's so much more interesting political drama in their lives that has gone unseen.