QUOTE(Tixylix @ Jun 8 2011, 01:25 AM)
I think they're around Grade 5-7 - I know one of them was in my Grade 5 book (2009-2010).
I'd say the range is broader than that, from relatively easy (doable at Grade 4,) to quite difficult (requires post-Grade 8 skills).
If you are looking for something a little easier (some pieces ... not all of them!) look at his 'Album for the Young'. That looks to me as though it was written as a tutor book for aspiring pianists - a musically superior tutor.