Twins can have sibling rivalry as much as siblings who aren't twins, partly because of people's misconceptions about how twins act.

Approximately one-third of twin births are identical twins, developed from a single egg that splits into two after fertilization. Fraternal twins, which develop from two separate eggs, comprise the remaining two-thirds of twin births, and are split evenly between same-sex twins and boy-girl sets.

Common Myths About Twins

Aside from the natural rivalry that arises between two children sharing the same parents at the same time, adults may unwittingly encourage competition between twins. Preconceptions held by adults and made known to the children almost guarantee that the children will sense the need to compete. Consider some of the common misconceptions about twins:

There will be a "good" twin and a "bad" twin.
One twin will be smarter than the other.
One will be a follower and the other a leader.

How Parents Contribute to Twin Rivalry

"Everyone stands ready to contribute to the mythology," says Patricia Maxwell Malmstrom, who elaborates on these and other myths in the book The Art of Parenting Twins: The Unique Joys and Challenges of Raising Twins and other Multiples . She suggests that parents think of their children's differences in positive terms, rather than letting negative labels become fixed.

"Only use good or neutral qualities or characteristics to describe them, like 'He's the chatty one,' or 'She's a watcher,'" Malmstrom suggests.

Even when parents avoid the myths, rivalry between twins comes up. As the mother of twin toddlers, AnnMarie Killam, host of the Bella Online Twins Channel sees it all the time.

"My twins first started trying to overpower the other when they learned that hitting each other would elicit a response from me. One twin would hit the other over the head, producing two results: his brother would cry and I would give him the attention by telling him 'no,'" she says.

"Another area of competition/rivalry occurred in the actual hands-on attention I give them," Killam continues. "It's gotten to the point where if one twin gets hurt and starts heading toward me for comforting, the other twin will run just to make it to my arms first. I usually give the unhurt twin a little hug to let him know I love him, and then pick up the one [who] is hurt and cradle him while kissing his injured area."

Developmental Delays and Health May Play a Role

Sometimes developmental difficulties, such as deficits in language and social skills, can foster competition. Maddie, a fraternal twin speaks fluently for a two-year-old and her language is easily understandable. Jimmy, her brother, is less easily understood and adults have to question him repeatedly before they can understand what he's trying to say. Jimmy shows his frustration by hitting his twin sister.

According to the National Organization of Mothers of Twins Clubs, Inc. (NOMOTC), twins are often born premature, which may account for a delay in their language skills. Even if the twins are not premature, developmental delays can occur just because there are two same-aged children in the house fighting for attention.

Studies show that young twins receive less directed speech from their caregivers, according to Jennifer Ganger, PhD, who initiated the MIT Twins Study and is director of the University of Pittsburgh Twin Study of Language Development. They also get less one-on-one attention. Both of these situations are thought to be partly accountable for the delay in language learning

Sometimes health considerations can account for developmental factors.

"What may have accounted for less interaction from our daughter Lindsay was that she had significant ear infections, which we later learned caused hearing loss," says Leslie Cattell, the mother of teenage twin daughters. "When people asked them 'What did you girls do today?' invariably, Laura was the spokesperson. Lindsay deferred to her. We thought it was personality differences, but when Lindsay had tubes put in her ears, we saw her little personality blossom dramatically. It turned out she had plenty to say!"

Some Positive Steps

It's sometimes difficult to remember that twins, even those who look alike, are separate beings. Twins, like all children, strive to be seen as individuals.

Cattell suggests the following tips:

Pay attention to individual preferences.
Cattell says that she and her husband would ask questions pertaining to their daughters' individual interests.

"We'd say things like 'Is this your favorite book, Lindsay?' or 'Laura, you really like the color green, don't you?'"

Make time for each child.
"We spent separate time with each child and encouraged separate time for each of them with their older sister and their grandparents. We shared their individual differences with their grandparents, which made it much easier when it came time to spend overnights or buy the twins gifts."

Make your own decisions about whether your twins should be in the same class or do the same extracurricular activities.
No one formula for school placement fits all twins at all times. Young twins who are still working out the balance of their relationship with each other benefit from starting school in the same class. There, in the comforting presence of their co-twin, they can learn to separate by participating in different activities with different groups of children. When twins are separated before they have learned independence they may feel grief or anxiety and be unable to concentrate on school work.

Cattell found that placing her children in separate classes worked out really well for them.

"Our children started in separate kindergarten classes and have remained in separate classes throughout school. This was very good for them because, since they look so alike, outside of school, they were often called by the wrong name. In school however, their teachers and classmates knew them as individuals and in the classroom no one forgot who they were."

"Listen to your kids," says Killam. "Their actions and their words will tell you what they like, what they don't like, what they are good at and what they need help with. Don't push the twins to be in classes together if they don't want to be. If they want to play the same sports, then great, but they don't have to."

Malmstrom concurs. "As long as children are choosing activities that are of true interest to themselves (not just as ploy to stay together), I don't worry. Life affords natural opportunities for different experiences. We honor their individuality best by letting them choose."