As Helene Mansfield, head of Croesyceiliog School in Cwmbran, puts it: "Some women may not wish to go for a post that is seen as time-consuming and all-absorbing."
As heads regularly work a 60-hour week, often filling in unnecessary forms and number-crunching, it is no wonder competent women teachers would rather take their talents elsewhere.
If recruitment figures are anything to go by, the same can be said of male teachers, who are much more likely to stick with senior posts that pay well and are less pressurised.
According to Olwen McNamara, one of the authors of Women Teachers' Careers, women are thinking more flexibly about their working lives, and that does not necessarily mean reaching for the top, it seems. A cannier sideways step into consultancy may make for a more fulfilling career and mean that mum is home in time to read a bedtime story.
Wales, the research says, has a fairer gender balance in teaching than the rest of the UK. This can only be a good thing, but it has to be accepted that women still face barriers in their bid for the top - some of which are biologically unavoidable. Later career breaks due to pregnancy for women in their thirties disadvantage them at a critical time in their working lives, says Professor McNamara.
But her research shows that the proportion of women entering the profession is up by 7 per cent. At primary level, women teachers still dominate, and at secondary level, where only a third of women are teachers, things are improving.
In light of this research, perhaps it should be asked why - despite constant calls to the contrary - men are not entering the teaching profession at primary level.
Boys, who are failing to match girls' achievement, need role models at all levels; yet they are are still being short-changed. Unfortunately, it seems this is not an area under such rigorous research, but it is one that might be more beneficial in the long term.