Boys will perform just as you expect them to, it seems. If you tell them they aren't as intelligent as girls and are less likely to do well in tests, that is exactly what will happen. So says the latest salvo in the battle of the sexes that has preoccupied educationalists for decades.

A study published at the British Educational Research Association conference tested two classes of youngsters. One (mixed) class was told that boys generally performed worse in tests than girls; lo and behold, those boys did exactly that.

In the other class of 10-year-olds no such information was imparted, and the performance of the two sexes in a reading test showed greater parity. This is in line with the Pygmalion theory of education, as highlighted in the 1968 US study Pygmalion in the Classroom, which showed that if you split pupils randomly into two groups labelled"improving" and "not improving", the "improving" group will improve and the other one will not.

So could the answer to the question that has dogged educationalists for years – how to ensure that both boys and girls perform to their best of their ability – be as simple as telling them that they can achieve? The answer is, regrettably, almost certainly not. After all, not all boys have been told they don't perform well in tests, yet almost universally they come in a poor second to girls.

It is worth looking at the issue in greater depth, though. And it may also be worth pondering whether there is, in fact, a dilemma to be solved. Why should we worry if girls out-perform boys? Fears over gender performance first came to the fore in the late Fifties and early Sixties: too many girls were being shepherded into the arts and humanities, or were being encouraged not to pursue a career at all because they would only end up looking after a man. A campaign group called Wise – for Women into Science, Engineering and Construction – was set up. It was modestly successful in persuading girls to look at these subjects as a career options, and in persuading teachers to press such options upon their female students.

But at GCSE level, girls still lag behind the boys in take-up of the three separate sciences. In England, Wales and Northern Ireland this summer, around 60,400 candidates taking biology GCSE were girls, and more than 69,000 were boys; in chemistry, there were 55,450 girls and some 66,500 boys; and in physics the gap was slightly wider. And gender stereotyping is most rife in take-up of the new diplomas pioneered by Labour. Relatively few girls choose subjects such as engineering and construction, while they abound in applications for hairdressing and beauty therapy courses.

On the whole, though, it is nowadays the education of boys – particularly white, working-class boys – that most worries educationalists. The accent switched towards worrying about boys' education in the early years of the Labour government that came to power in 1997: a report by Ofsted, the education standards watchdog, said – in uncharacteristically blunt language – that boys were spending more time on the "three Fs" than the three Rs. The three Fs were characterised as "fighting, football and f***king".

The report said that, in times gone by, when there were plenty of manufacturing and manual jobs, boys "celebrated the tough physical manual labour of their fathers and the macho culture in which men were main wage earners, the future breadwinners. Facing the loss of traditional male employment and finding themselves in a competitive school culture ... the macho lads responded to their academic failure and lack of employment prospects by celebrating the three Fs." In a nutshell, years of encouraging girls to think career-wise coincided with years in which most boys' traditional vocational career options dwindled.

The results even at that stage showed that two-thirds of girls were obtaining five A to C grades at GCSE, compared with just 50 per cent of boys. The research showed that the gap was emerging at an ever-earlier stage, with 83 per cent of girls reaching the required standard in reading by the age of seven, compared with just 73 per cent of boys.

The answer, under the regime of Labour's first Education Secretary, David Blunkett, was to try to make the curriculum more appealing to boys. More action books rather than works by writers such as Jane Austen and William Thackeray – traditionally the set texts for GCSEs and A-levels – should be used in schools, it was argued. Substitutes such as Treasure Island, Sherlock Holmes stories and even Raymond Chandler's Philip Marlowe novels were suggested as alternative set texts to switch boys on to reading. Male role models – such as the footballers Ian Wright and Tony Adams – were drafted into schools to support reading campaigns. But by 1999, figures showed that boys were faring worse than girls in every exam – from the national curriculum tests for seven-year-olds up to A-levels. Only in a handful of subjects, like maths and some of the sciences, were the tables turned. In the following decade girls were to steam ahead at university level, too.

The biggest leap in girls' performance, though, occurred in 2002 – the first year that the new syllabus for A-levels, with more emphasis on coursework, was examined. "Boys tend to do better in exams," says Professor Alan Smithers, director of the Centre for Education and Employment Research at Buckingham University. "Girls apply themselves to coursework and work more consistently throughout the year." Many educationalists at that time talked of the curriculum being "girl-friendly". Most observers, for instance, backed Smithers in believing that girls flourish in the more methodical approach needed by coursework – which by then had become the key feature of both GCSEs and A-levels. There is an attempt, now, to turn the clock back. Independent schools, in particular, are opting for the international GCSE, rather than the home product. It is an exam based on the "traditional" values of the old O-level, with a ban on most assessment through coursework and a focus on end-of-year exams.

Similarly, in A-levels there is a move away from modularisation – under which the two-year syllabus was cut down into six constituent parts, and pupils went seamlessly through from one module to the next. It was cut to four modules for this year's students, and further reforms are planned by the Education Secretary, Michael Gove, to bring back a more traditional ethos. These include getting universities more involved in setting papers, in the hope that they put back more "deep thought" into the A-level syllabus. Just how that will impact the relative performances of boys and girls is unclear, although those who have argued that boys are late developers, and can come up trumps when they realise education is about to get serious, took heart from an analysis of this year's independent school results.

It showed that boys had at least scored one victory over girls. They were ahead on the percentage of candidates securing three straight A* grades at A-level. This was 6.8 per cent of total papers submitted by boys, compared with 5.8 per cent achieving that among the girls. An alternative way, meanwhile, of dealing with the gender gap is advanced by proponents of single-sex education: teach students separately. Some mixed schools, notably Shenfield, a comprehensive in Essex, have even supported that argument by teaching them in separate classes in certain subjects. The Girls' School Association president, Gillian Low, sums up the argument: in a single-sex classroom, girls "are more inclined to stand up and make contributions in class. They're not thinking about what the boys' reaction will be." Similarly, supporters of boys-only education say there is less pressure on them to play to the gallery in single-sex environments.

These arguments, though, ignore some of the social consequences of teaching boys alone. According to a study by the Centre for Longitudinal Studies at London University's Institute of Education, boys who have been to single-sex schools are more likely to end up divorced than those taught in a mixed environment (37 per cent as opposed to 28 per cent). "There does seem to be a picture of boys from single-sex schools finding it more difficult to sustain a relationship with the opposite sex," the report concludes.

Does it matter, though, that girls are now performing better than boys in exams? "I'm not sure," confesses Professor Smithers. "The issue is whether we're allowing boys and girls to develop to their full potential. In particular, that was highlighted by the old 11-plus (which determined who went to grammar schools). Girls consistently did better than boys, so boys were allowed in on lower marks – something that wasn't really made known at the time. I think we ought to look at the nature of testing and examining, to make sure we've got the proportion of coursework and final examination right. I don't think we should want to equalise the outcomes of education, though. It doesn't bother me that girls don't appear to like physics very much but are more steeped in literature than boys."