QUOTE(Aquarelle @ Jul 8 2009, 04:45 PM)

I think woodwind scales are fiendishly difficult. I've just had a Grade 2 recorder player who simply forgot the lot in his exam. He does have learning difficulties but even so I think recorder scales are much more difficult than piano where at least the fingering is logical and you can see what you are playing as well as hear it.
However, I suspect that by the time each instrument has got to Grade 8 the unevenness of the pacing through the grades is ironed out.
^ I think Aquarelle gets it in a nutshell.
As a lousy pianist, a reasonable violinist and a fairly competent flautist, I find piano scales by far the easiest, violin scales not difficult to work out (though difficult to play in tune!) and flute scales a heck of a lot of work which I have become reasonably good at by dint of much practice.
And if you look at the G8 requirements, the differences are much smaller.
Some of it also has to do with range... for instance, I believe the clarinet (and certainly the violin) has several 3 octave scales that appear lower down the grade scale, whereas flute only expects 3 octaves scales off C and those only in G8. Looks unfair? Simple reason is that the expected range of a G8 flautist is only that 3 octaves, and even really good flautists don't range much beyond that (I think you can get about a 4th higher? but it's pretty tough for most), whereas for clarinet and violin with wider working ranges, it's not unreasonable to expect 3 octave scales considerably sooner.
Taking into account that different people find different things easier or more difficult, in my experience the actual difficulty of learning the requirements (as opposed to the number of keys or patterns learned) is pretty even, or even in some cases the requirements with fewer actual scales to learn are still more difficult.
FWIW, the most trouble I've ever had with scale requirements was for treble recorder G1! Only three keys, yes, but with the forked fingerings, the lack of keys to help out, and the fact that some of the fingerings don't feel that logical, I still struggled, especially with the slurred scales and arpeggios. Give me a couple of dozen piano scales to learn any day!