I've noticed that. In gr 6 you have to play the scales in ALL keys, but no ones in 3rds, I guess. In gr 7 you play similar motion and 3rds, but in only have of the number of keys you played in gr 6. In gr 8 suddenly you have to be able to play them in 6ths. And you have to be able to play all chromatic scales in 3rds. The stuff from the earlier grades aren't in. I think the AB should make an improvement. Gr 8 students should be able to play scales in all keys. I don't want to disappoint you all, but it's odd if you don't have to play in all keys because you did play them in gr 6, regardless of you didn't do 6ths, 3rds, etc. And other examination systems usually make people doing the last grade play scales in all keys and ways.
The 6ths and 3rds. should be introduced in an earlier grade. But maybe not in all keys at once. Just a few keys. That way, I won't feel studying 6ths in gr 8 extremely difficult, because I never tried. Maybe the AB wanted it to be convenient, so you don't have to have a specific group of keys for a type of scale?