Women in Engineering and STEM Fields

Right now, only 18-20% of engineering students are women, and only 15% of the engineering workforce is complied of women. This is an improvement over the 1980's where just over 5% of women were engineers. But why is engineering still such a heavily male dominated field? Why have women been prevented in making major change in this boys club?

Some different Ideas are currently being explored including, but not limited to:

• How Math attitudes from an early age associate Male with Math making it harder for women to associate themselves with Math and STEM: There is a disconnect with technology and the idea of women 
• Lack of Role Models in Science=Lack of confidence in abilities
• A self fulfilling prophecy: girls believe they can't be good at math, therefore they aren't 
• The way people 'do/perform' gender. The way women feminize engineering by centering it around helping people, making it socially acceptable for them to participate
• This prevents acceptance of women into more technical engineering fields, preventing advancements 

I am looking for more information about how society stereotypes prevent women from making the engineering choice: why is this choice so much harder for females?