The whitewashed classroom at the University of California, Berkeley, looks quite ordinary. But the questions from the students are extraordinarily emotional and plaintive.

"You've had a child before you have tenure, which I heard is a really risky thing to do," one female student said to the speaker, an alumna who chose to accept a faculty position at a small university because she thought it would be easier to have a child there. Her five-month-old boy sits fidgeting on her lap.

"It seems to me that most women at high-powered universities don't have children. Do you perceive that to be true?" asked another.

These female doctoral students at one of America's top universities symbolise a topic suddenly at the forefront of US ÖйúAƬ.

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Even as large numbers of faculty are getting ready to retire, women are being discouraged from careers in academe because the requirements of tenure make it hard to have children.

The average age at which a woman gets her PhD is 34, and she is likely to get tenure at 40 - if she meets the research and publishing requirements.

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Research at Pennsylvania State University shows that most women who choose to pursue a career in academe avoid having children. Far more opt for jobs outside ÖйúAƬ. Women make up only 10 per cent of full-time US faculty in engineering, 26 per cent in maths and 16 per cent in physics.

This is despite the fact that 42 per cent of doctoral recipients are women.

"Working parents in general, but women with children in particular, are being disadvantaged in the academy because the tenure path coincides with the final years for women to have children," said Kathleen Christensen, who oversees the issue for the Sloan Foundation.

Pressure to change the system has gained momentum from a series of $250,000 (?197,000) grants awarded by the foundation and the pressing need to attract new faculty.

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The foundation's "accelerator grants" have been made to the University of California, Berkeley; Davis; and the universities of Duke, Lehigh, Florida and Washington to further develop existing programmes that are seen as examples of how institutions can make it easier for women to balance family with a career in academe.

Schemes include making money available to cover for female faculty on maternity leave, encouraging tenure committees to be more flexible about publishing requirements and training department chairs to be considerate of such matters.

Some critics perceive department chairs and older female faculty as being among the most resistant to change, having survived the tenure track themselves.

Claire Van Ummerson, vice-president of the Center for Effective Leadership at the American Council on Education, said: "You have women who gave up having children, or gave up even marrying, especially in the sciences, and they're feeling some regret over the decisions they made. Now they see people coming along and getting help. And that doesn't sit well with them."

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And this makes the speaker in that Berkeley classroom, Kristine Lang, a sceptic. "I'll tell you what makes me angry," Dr Lang said when the students had gone. "What makes me angry is, let's say you want to have a baby and you want to take six months off. Because you want that time, you're screwed."