One of the reasons for the lack of diversity in the Core-STEM workforce is the leaky pipeline into these careers.
Many girls decide at about the age of 10 or 11 that STEM subjects are not for them. By the time they get to A-Levels, a time when girls and boys are particularly vulnerable to peer pressure, the number drops even further. This is despite the fact that the hard sciences are compulsory for girls at GCSE.