Girls are still outperforming boys at all levels of the curriculum, it was confirmed yesterday, following the publication of exam results for local authorities across Scotland.

Despite the adoption of a variety of measures to raise standards among boys, from single sex classes to regular testing, the Scottish Qualifications Authority (SQA) figures show no signs of the gender gap closing.

This year, 30% of boys achieved five or more Standard Grades at credit level, compared to 38% of girls. At Higher level girls again performed better, with 25% gaining three of more Highers in S5, compared to 19% of boys.

The so-called gender gap in attainment is not a new phenomenon but has proved particularly difficult to tackle, and there are differing theories about why it exists.

Girls, it is said, mature earlier than boys and are therefore better able to concentrate on their studies, while boys have to deal with a more difficult transition through the teenage years.

Peer pressure is also said to be a key factor, with boys heavily influenced by contemporaries' views of what is "cool" and therefore reluctant to shine in class at the risk of being bullied or branded a teacher's pet.

Another suggestion is that the learning techniques of boys are better-suited to a succession of shorter-term targets than a long course followed by an exam.

Yet another theory suggests stereotypical expectations that boys will be daring and active and girls well-behaved may be self-fulfilling.

Eric Wilkinson, professor of education at Glasgow University, has argued that the problem is one of motivating boys, who are not engaging with the learning process in the same way as girls.

Yesterday, Dr Alastair McPhee, a reader in educational studies at Glasgow University, said the issue was not just about gender.

"There is evidence that working-class girls do not perform as well as middle-class girls, while middle-class boys can catch up, so this is as much a class-related issue as it is about gender," he said.

Dr McPhee also believes local authorities need to work harder to address the issue. "There are a number of successful strategies employed by some schools to combat gender inequalities, but these are not replicated across all councils.

"There is a sense that some local authorities are not taking this seriously enough," he added.

However, Judith Gillespie, policy development manager for the Scottish Parent Teacher Council, said analysts should not get "too hung up" on the gap.

"This is nothing new and has been there since the days of grammar schools," she said. "It doesn't mean that boys as a group are underachieving in everything because boys can be in the top group for some things and the bottom group for others, whereas girls perform well in a range."

Yesterday's SQA figures also highlighted once more the stark impact of deprivation on exam success.

As previous studies have shown, council areas that serve some of the most deprived parts of Scotland, including Glasgow, Dundee, North Ayrshire and West Dunbartonshire, are once again largely outperformed by those in the wealthiest areas.

In Glasgow, 22% of S4 pupils achieved five or more Standard Grades at credit level compared to the Scottish average of 34%. However, there was some improvement at Higher, with 15% of S5 pupils getting three or more exams compared to 14% last year. The national average is 22%.

In contrast, the best performing councils, including East Renfrewshire, East Dunbartonshire and Stirling all have much lower proportions of pupils on free school meals. In East Renfrewshire, which achieved the best results this year, the figure for free school meals is just 8.3%.