The Surprising Reason Girls Aren't Learning to Be Leaders A Harvard study found that girls tend not to support other young women.

 -- For the last few decades, women have been breaking professional barriers. But a new report by Harvard’s Educational School reveals there’s a hidden barrier teen girls are running up against.

“Girls are facing biases from many sources, from teen boys, from some parents, and they are facing biases from each other,” Richard Weissbourd, co-director of Harvard’s Making Caring Common Project that conducted this study, told ABC News.

The startling result is that these biases could be holding girls back from succeeding.

“We have made a lot of progress in terms of gender equality but we still have a long way to go,” he added.

The study of 20,000 students showed only 8% of teen girls preferred female political leaders.

“Males have always lead, so I guess we’re kind of used to it,” one 17-year-old girl said.

“Right now it seems to be mostly a male-dominated sphere,” added another.

What’s more surprising is that even some mothers appear to be biased, supporting school councils more led by boys.

The report also reveals girls tend not to support other young women saying they feel threatened by their successes in school. Weissbourd believes girls need to start working collectively to fight biases.

“Emphasizing girls’ solidarity is really important,” he said. “That is an important message for parents to send to girls.”

Rachel Simmons, author of "Odd Girl Out" and co-founder of Girls Leadership, says these findings are amazing, but she’s not really surprised by them.

“Even in this day and age, we’ve given girls every opportunity but our attitudes still have to change,” Simmons said on “Good Morning America” today. “We’re still giving girls messages to look at each other as threats. Think about the media images of ‘Mean Girls’ and cat fighting. Girls are not looking at each other for support, and they’re also feeling so insecure about how they look. Think about Instagram and social media. They’re feeling like, ‘I’m not as pretty as the next girl’ so they’re not supporting each other.”

Simmons offers ways for parents to help break these patterns of gender bias:

Change the chores.

"Research shows that chores can be distributed in really gendered ways," she said. "That means we tell boys to mow the lawn and girls do the dishes. Change it up at home. That’s a big thing parents can do. Let boys do some caregiving because beliefs and attitudes start very early and parents can help kids change it very quickly and very early in the home."

Words matter.

"Another thing is change the way we talk to our kids," said Simmons. "If you have an outspoken girl, do you call her bossy, or do you say, ‘I’m so glad you spoke up’? If you’ve got guys at home who talk about doing things ‘like a girl’ as if that’s a weak thing to do, we’ve got to say ‘knock it off.’ That’s not the way to talk."

Check your bias.

"We all have our own biases. I have a 3-year-old daughter and when she doesn’t want to wear a dress, I get a little bummed out about it," she explained. "Again, every parent has to look at their own biases. What toys are we buying for our kids? Are we buying girls the makeup kits and boys the science kits? It’s ok to do that, but change it up a little bit."