Arduino will not recognise USB ports on my Mac running Sierra
I spoke to a very clever friend who has had similar problems. The answer lay in downloading the FTDI helper package not just the driver.  If anyone else is having a similar problem the website is 

https://www.ftdichip.com/Drivers/D2XX/MacOSX/D2xxHelper_v2.0.0.pkg

I downloaded it and now my lilypad and USB port is recognised by the Arduino software.

Just in time for Thursday.

Thanks to all who tried to help.

K