On a sultry day in the garden of a hotel in the affluent Paris suburb of St Germain-en-Laye, 20 female executives are practising saying "non". Their imaginary interlocutor is "Jack", a bullying boss who wants to spend the weekend playing golf and is trying to offload a project he has failed to complete.

To make it clear they reject Jack's ill intentions, they are using the KISS technique, a not remotely sloppy marketing tool that stands for "keep it short and simple". Working in pairs, they take it in turns to play Jack - a role they take to with gusto - and his female colleague. Having listened to his request, they are encouraged to look him in the eye, explain briefly why it is impossible, and tell him in so many words: "No can do, Jack."

Communicating effectively is at the heart of this two-day women's leadership course run by Diafora, a Paris-based consulting firm that helps companies develop a culture that attracts and motivates women.

The premise is that women and men communicate differently and that failing to appreciate the differences can hamper women's progress in male-dominated workplaces.

JoAnne Freeman, one of the facilitators, runs through a list of "strong" phrases such as "The way to go", "I'm convinced" and "immediately", and a list of "weak" phrases such as "I guess I could", "perhaps" and "I'm sorry".

She argues that women are still conditioned by expectations of deference drilled into their mothers by such memorable 1950's publications as the Good Wife's Guide, in which "a good wife always knows her place".

This conditioning can undermine the self-confidence, assertiveness and risk-taking required of prospective corporate leaders.

Women have a tendency to use weak rather than strong words. Saying: "I really don't know much about this but I think we should..." is an impact-killer, according to Diafora. Powerful, concise messages - whether saying "no", negotiating a deal, giving feedback or asking for a promotion - are what busy bosses understand and appreciate.

Telling people what to do and delegating work are more difficult for women, says Ms Freeman. "They don't want to be seen as bossy or aggressive." But they need to learn to speak out; the first person to speak at a meeting is the one who gets noticed.

Leadership courses for women are mushrooming as companies seek new ways to retain their female high-flyers and staunch the mid-career brain drain. Business schools are also getting in on the act. This wide-ranging course on "strengthening influence and impact" has attracted women from across Europe, working for companies such as Alcatel, Deloitte, General Electric, PwC and Schlumberger.

One delegate, a finance director in a large industrial company, illustrates the unease that persists when women reach the top of heavily male companies. As she was being recruited to her senior management job, she was told she had the best profile, "except that, as a woman, they were concerned that I would not feel comfortable because they were all men". This woman has already achieved power, albeit on difficult terms.

But "power" and "politics" are words that many women shy away from, says Avivah Wittenberg-Cox, Diafora's founder.

She is right. When a photographer from a French newspaper arrives to take a picture of the delegates, Ms Freeman suggests a "power" pose, with fists clenched and knees bent. Several women demur. "That would come across as rather aggressive," says one.

At a very different course in London, a group of male and female managers have gathered to discuss how best the genders can work together. But here the female dislike of "politics" surfaces again. Sue Henley, head of diversity at Merrill Lynch in Europe, explains how women at the investment bank balked at the idea of a programme aimed at honing their political skills. She found a solution. "Women didn't want to do politics," she says. "We changed the word 'politics' to 'profile', and that was fine."

Words, however, are only one part of communication. On the French course, we are told that what you say accounts for only 7 per cent of how you communicate - an oddly precise figure - and that how you look and sound are far more important. Presentation, posture and pitch of voice all count strongly. Standing with your legs crossed or speaking in a soft, high-pitched voice does not make a positive impact.