Research published this month by children's development agency Plan ups the ante in the gender and education argument.
According to "Paying the Price: The economic cost of failing to educate girls", gender gaps in secondary education cost their retrograde countries annual growth to the tune of $92 million.
The figures, which are the result of an analysis of U.N. and World Bank statistics, take further widely accepted ideas that an educated female population yields development-friendly benefits such as healthier children and small families.
The agency hopes that shifting the argument for female education away from traditional moral goods such as equality and human rights and placing the emphasis on economic realities instead will help concentrate policymakers' minds on measures that will encourage girls to stay in classroom for longer.
"They're all valid points, but you have to put it in terms of "What's in it for me?'" says Gary Walker, Plan's director of communications.
Putting the case in terms of hard cash is likely to be particularly persuasive as developing countries
contemplate shrinking aid budgets and rising food prices, he thinks. "If there's any reduction in aid, educating girls allows you to tap into resources that are self-sustaining," he says. "It's a win-win situation."
While the education gender gap is narrowing, two-thirds of countries still have a considerable way to go before parity in secondary school attendance is achieved, according to a report from U.N. children's fund UNICEF, Progress for Children 2007.
One country where the penny seems to be dropping is India - which, according to Plan's research, misses out on growth of $32,636 a year. Under a new scheme, authorities are now paying girls in Mumbai to go to school. For every day they attend, state school girls get 1 rupee - about 2 U.S. cents - while boys get nothing.
The initiative is part of the government's drive to improve girls' education record, an aspiration bound up with the need for large numbers of well-educated employees to staff the service industry at the heart of India's burgeoning economy.
But so far, the results are disappointing. Not one of the city's 220,000 girl pupils has a full attendance card, while the register of one school shows that, on average, girls missed 20 to 70 days in the last year.
The reason, locals say, is not hard to find. A daily rupee is simply not enough to act as a finanical incentive for families who need to send their offspring out to work, particularly once adolescence brings children significant earning power. In a country with a healthy recycling industry, children can easily supplement the family income by gathering plastic bags and other rubbish and selling it for cash.
One school that is bringing in the girls is Free Schools India , a private, non-fee paying girls' school in the village of Chakarsi, in the Uttar Pradesh region northeast of Delhi.
It began in 2004 when NGO worker Joanna Harma and community leaders in Uttar Pradesh realised that, with children spending their days stitching footballs to earn money, there was a real need for a local school.
Consultation with families in Chakarsi about what kind of school they wanted revealed a surprising hunger for girls' education. "The people asked specifically for it to be for girls," says Harma, explaining that lack of access to transport and concerns about male teachers made parents reluctant to send their daughters to nearby government schools.
"They wanted a secondary school in their area that they could feel confident about sending them to," she says.
Today the school has 310 pupils between the ages of four and 14, with more queuing up at admissions time than it can accomodate.
Harma, now vice-president of Free Schools India, thinks that the school's attraction for all but the most abjectly poor is nothing more complex than the good education it offers - in sharp contrast to state schools, where teachers often abandon classes to work on their land. Unannounced visits to government schools for her PhD research showed how little real learning took place in the state system. "I never found a teacher teaching, apart from one teaching assistant," she says. "Usually teachers were sitting there with their feet on the desk, and the kids were mucking around, playing or fighting."
"I think attendance has more to do with the quality of what's on offer than anything else, at least in this area," she adds.
Changing social trends also give hope that girls' educational fortunes are on the up. According to Free Schools India's founding board member Gaurav Siddhu, uneducated rural families are increasingly setting a value on educating their daughters, even if they are destined for marriage and motherhood rather than the workplace, because of the social kudos it carries. "When people see neighbours' daughters acting better, they say, 'I want my child to act like that. I want my child to speak English, to act more refined.'" he explains.
But he is wary about using the kind of hard-nosed economic arguments that feature in Plan's research to improve girls' school atttendance.
"When I talk to parents, I only talk about child development. Although we follow the national curriculum which is job-oriented, we don't use that as a reason why parents should send a child to school. We can't guarantee them a job," he says.
And while he agrees that economic arguments may be effective tools for lobbying and advocacy, he questions whether the economic models they're based on - which can yield different conclusions depending how the data is used - are really the best way to further the cause. "Right now we should be talking about universal, free, quality education," he says.
It seems that, for some, it's the old fashioned moral arguments that remain the best ones.