Hi Susan,I am not disputing your teacher.... but...... classical music and Irish music are not the same. (9/8 doesn't really exist in classical, but it does in Irish music.)
slip jigs can be hard to define.... but they do have a certain "feel" about them. and this particular tune has that "feel".
But just for the fun of it I'm going to put the tune into the computer both as 9/8 and as 3/4 and let you make up your own mind which sounds closer.
And yes, most of Clannad's stuff is very good..... although I have to admit I do prefer the earlier stuff.
slainte
alison
PS I do have a lot of classical and theory experience too.