Girls' expectations that they can "have it all" may be overly ambitious and they should not feel guilty for taking time out of future careers to raise children, a leading headmistress said today.

Schools need to teach teenage girls about the realities of juggling a career with having children, and that life is more complicated than "having it all", according to Jill Berry, president of the Girls' Schools Association (GSA).

While it is "healthy" for girls to aim to have "a flash sports car with a baby seat in the back", they need to realise that they will face challenges and have to make choices in life, she said.

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Speaking ahead of the GSA's annual conference in Harrogate next week, Mrs Berry told the Times Educational Supplement: "They will need to realise that there may be times when they might not want to work, or they might want to take a lesser job because their priorities have changed. It is important that they leave school at 18 with their eyes open."

Mrs Berry said that girls should "stop beating themselves up" if they cannot juggle a career with being a wife and mother at the same time.

"Your priorities shift, but you're not selling out - you are facing reality and trying to be realistic about what you can achieve and you should stop beating yourself up about it," she said.

Most women are unable to "keep all the plates spinning", Mrs Berry, who is also head of Dame Alice Harpur School in Bedford, said.

Message in recent years have led girls to expect that they can "have it all", but this has made life seem simpler than it is, she said.

But she said girls should still be taught that they can be independent and compete with men in the workplace.

"When my pupils try to wind me up by saying they plan to marry a rich man to support them, I ask them 'what if he runs off with the au pair?"'