The BBC story "Science 'not for normal people'" outlines research which indicated one reason for many students opting out of science at school. Apparently, teenagers thought that scientists were not 'normal young and attractive men and women'.
That research was conducted in England, but I reckon Scottish teenagers (and many adults) would share the view that scientists are a bit odd and not the sexiest specimens around.
There are a lot of factors that influence the choices made by teenagers when choosing their subjects for exams/qualifications at age 13, but parental influence is a key one, and ideas about future jobs are another. Widespread public perception that scientists are unattractive nerds is a significant hurdle to overcome, and makes it essential to have activity and campaigns to persuade children and adults otherwise.
NESTA does some good work on Science education projects and the public communication of science. For example, Planet Science is a great resource.
Scottish Executive Education Department has also supported science education in Scottish schools through initiatives such as 'Improving Science Education 5-14'.