I'm still at University but have got a years experience in the field, Civil Engineering, and at uni there seems to be a lot going on encourage girls to become engineers even to the point where they get extra grants and such not available to me and other men JUST because they are female.
Whilst we need to make sure no one is discouraged to take a subject, I don't think the right move is to encourage them like my University does.
Just wait until you get into employment. "Sorry, we are only hiring women at the moment". Unfortunately the "golden skirt" Is a reality in many larger companies in engineering and science disciplines. Unfortunately that trickles up and tars all women with the same brush. "Did that new girl get the job because she was as good as us/best person for the job, or because she was the best woman that applied...?
As mentioned, the issue needs to be dealt with at the early senior school level, to persuade girls to do more physical sciences at A-Level and subsequently STEM subjects at degree level. You're never going to have equal male and female graduates in jobs in certain subjects when only 1/5 of the graduates are women, although remarkably many larger companies do seem to have close to a 50:50 M:F ratio in their graduates...