In reply to TomGB:
Glentress is an obvious choice from Edinburgh and Ridelines mtb is popular. They do beginner courses (and of course much more technical ones as things progress).
Comrie Croft has some easy stuff for teaching (and a nice setting including a camp site next to the trials if you want to make holiday of it), but I think, say for the likes of a nervous beginner if that is relevant, it would be best at Glentress on the really easy stuff which is more extensive.