Hmm, my concern with the accompaniment tracks is that sometimes they really do encourage you to crank up the speed long before the fingers can really keep up. Risky thing to try, in my opinion!
As for listening to the pieces before learning them, I never did that. In the case of some of the later grade Baroque pieces, I frankly think the interpretations given on the CD are a bit lacking. That said, I guess they don't want to encourage student after student to play the ornamentation and dynamics they heard on the CD, rather than coming up with their own. After all, particularly in the case of Baroque music (and perhaps jazz pieces too, though I'm less familiar with the genre) the interpretation is half of the performance, and the sheet music just a framework to start with. (Or that's how I see it!

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The CDs didn't exist when I did the lower grades. I would hope though, that students listening to them would feel inspired by the higher standard (they are recorded by professions, after all!) rather than demoralised that they can't reach those loftly heights! I guess it might be hard for young children to relate, but still...
Thought: Would a CD of more authentic recordings be more or less useful? Namely, one containing recordings by G1, G2 etc level musicians, rather than pros?