In 2001, the Welsh Assembly gave itself a year in which to make a major impact on this gender gap. But results for 2002 show that, in both primary and secondary tests, girls continue to achieve better results than boys.
This is particularly evident in Welsh-language national tests used to in Welsh-medium schools. At key stages 2, 3 and 4, the gap increased significantly.
Edwyn Williams, general secretary of UCAC, the Welsh teachers' union, believes that this can be explained by the growing number of children from English-speaking backgrounds who attend Welsh-medium schools.
"A lot of pupils are sitting Welsh tests, even though they are second-language learners," he said. "And girls tend to do better at languages than boys, especially earlier on."
No other subject tested showed such consistent under-achievement by boys.
At key stage 2, the gender gap closed slightly in maths and English.
Targets were met in both maths and science at key stage 3.
Since devolution in 1999, there has been an increasing demand for Welsh-speakers. In a growing number of jobs, an ability to speak Welsh is essential.
But, despite the Welsh Assembly's efforts to promote the language, pupils consistently fail to achieve top grades in Welsh exams. This year, only 20.3 per cent of pupils sitting A-levels in Welsh as a first language were awarded grade A: well below the average of 25.2 per cent.
* Plaid Cymru will abolish key stages 2 and 3 testing if it wins the forth coming Welsh Assembly elections, party leader Ieuan Wyn Jones announced this week.
"On May 2 a Plaid Cymru government will abolish tests at key stages 2 and 3," he told a meeting of party members at Trinity College, Carmarthen, this week.
The Labour-led Welsh Assembly has already abolished key stage 1 tests .
But, say Plaid Cymru, consultation has revealed little support among Welsh educationists for any national testing.