Dear Tim.
Many thanks for the comments on why the Army Apprentice School/College might have adopted the Black Watch (Government Tartan).
Indeed there is the distinct possibility that stocks of kilts may have been available after the finishing of National Service.
My request was really to find out why the Black Watch Tartan was worn by the School/College and was there a connection with the Black Watch.
As I was unaware of the colours of the Government Tartan being that of the Black Watch since something like 1739. I tend to think that the Regiment adopted the Government Tartan as being readily available possibility because of the reasons you mention.
I am more than happy to think that as there seems to be no actual connection with the Black Watch as far as I can ascertain by the School/College it is more than likely that they adopted the Government Tartan from the forming of the Pipe Band in 1960.
Unless someone else can tell me differently !!!!!!!!!!!!!!!!!!!!
With my kind regards
Chris Walker
www.signalsbadges.co.uk