"The argument for coeducation is that it is not natural to segregate the sexes and it is not the same as in a normal family. I would argue that, having a son and daughter, boys' and girls' interests are different between particular ages," Mr Spawforth says.
He believes girls mature faster between 12 and 18, physically and intellectually. Boys are demanding but girls are likely to dominate both academically and socially. "At the ages of 13 and 14, girls are significantly ahead of boys and there are indications that boys feel threatened and develop a sense of non-achievement. Some schools in the state sector have found that where they can afford to do so they are actually teaching boys and girls separately in the middle school."
Mr Spawforth challenges the assumption that coed schools avoid gender stereotyping when it comes to subject choice. Evidence to the contrary suggested there was a polarisation with boys regarding maths and science as their province and girls as interlopers. Merchiston Castle has close links with several girls' schools and pupils meet for drama, debates, music and dances.
Merchiston boys appear to share their head's view. Shane Corstorphine, the head boy, fears that introducing girls would prevent the school fielding seven senior rugby teams. Andrew Roger, aged 17, is worried that boys might not be willing to speak out in class. Phillip Reid, aged 14, thought boys would be annoyed if girls outdid them .
Shane admitted boys might smarten up their appearance with girls around. "If the school was coed and you were going out with a girl, you would definitely make an effort not to have a bad hair day."