In the five years to 1996, teenage conceptions dropped 12 per cent across the US - a result, some claim, of setting up "virgin clubs" in American schools to encourage young girls to say no to sex. The fall among black women aged 15 to 19 was even sharper, down 21 per cent.
In Britain the rate at which women aged under 20 who are not married gave birth rose when Baroness Thatcher was prime minister, but has since fallen. There was an increase between 1995 and 1996, though no more than the general rise in fertility for all women. Teenage single mothers - despite periodic outcries in the media - form an ever smaller proportion of all single parents.
But rather than slogans about the coolness of virginity, social scientists here are more taken by suggestions that it is tougher American rules on child support by fathers that have cut teenage pregnancies.
This contention is backed by evidence from American inner city areas that the proportion of teenagers having sex who use condoms - contraception where the man may take the lead - has markedly increased.
Sarah McLanahan, an American researcher currently at the Centre for the Analysis of Social Exclusion at the London School of Economics, said "child support policies seem to be pushing in the right direction," adding that the American evidence put into even starker relief the "disaster" of Britain's Child Support Agency, which is now undergoing its third re-launch amid continuing Parliamentary criticism about its performance.
The importance of the American evidence is that it kills the idea - fashionable on the political right - that there is a tendency in modern societies towards social fragmentation and family breakdown.
According to Kay Wellings, a demographer at the London School of Hygiene, this may provide backing for New Labour's contention that getting more young people into work or job training will affect other aspects of their lives - including the desire to have children early. The American evidence suggests that access to jobs encourages young women (and men) to think twice about having babies early and leads to a more "responsible" climate.
"It's too simple to say `welfare reform works'," says Professor McLanahan. "It's more policies that push with the grain of what young women themselves want for their lives."
Teenage sexuality has lately been an American preoccupation with surveys showing that over half of 16-year-old American males have had intercourse while a quarter of all teenagers who have sex in any given year contract a sexually transmitted disease. Anxiety has focused on the way the children of teenage mothers themselves become young mothers and a cycle of inter- generational dependency on state benefits gets under way.
After President Bill Clinton - hardly a role model in matters sexual - made America's high levels of teenage pregnancy a policy focus three years ago, a National Campaign to Prevent Teen Pregnancy was launched. Isabel Sawhill, its director, claims success in "convincing teens that delaying sex may be a better idea, even cool".
Ceridwen Roberts of the Family Policy Studies Centre says British experience confirms that "educative and informative campaigns" are likely to work better than moralising. The British emphasis is on practical factors, including contraceptives. Anne Weyman, chief executive of the Family Planning Association, says young people need the skills and knowledge to use contraception but also the wish to control their fertility - and that depends in part on what the schools teach and on what the NHS makes available to them. The bid by campaigner Victoria Gillick in the early Eighties to prevent doctors dispensing contraceptive advice to teenage girls had a marked effect on the climate and may have contributed to the sharp rise in teenage conceptions during the Eighties.