when I had lessons, I was doing 1-2 pieces at a time.
Now I'm doing 1 at a time. I don't think you can do well with 5 or 6 at a time; you'll get ideas mixed up and stuff. Or maybe not, but I don't see the point in studying too many at the same time.
Good luck on ur grade 10 exam 
what pieces are you playing?
So my routine isn't normal? :| What if I forget my other pieces?
Sometimes I don't know what my teacher is going to ask for the next week... she'll start getting worried about one piece, and ask me to play it even though I havven't practised it much. So that's why I tried to juggle them all, because sometimes I don't know what she'll ask for. Thanks for the luck, I'll need it although I'm not even thinking about piano exam prep yet =/ (School... on the other hand :S )
These are the pieces I'm actually playing at the moment/attempting to juggle. I started out with many more, especially from list E!!! , but they just got ignored.

Maybe someday...
Bach Prelude and Fugue in Eb Major, BWV 876
Bach French Suite in G Major, Allemande
Haydn Sonata in D Major Hob XVI:33
Chopin Nocturne in C sharp minor, op 27 no 1
Chopin Nocturne in b flat minor, op 9 no 1
Faure Barcarolle in Ab Major, op 44
Muczynski Preludes Op 6, no 1 and 6
Rachmaninoff Etude Tableau op 33 no 8
Heller Prelude in c sharp minor
Haberbier Serenade op 33 no 5