i think my teacher wanted our works to be marked by someone who didn't know us, so it would be much more objective. i guess that seeing she's watched us develop and work on ours for so long, and she knows our progress, it would be difficult to mark. so they were sent off to one of her friends...
unfortunately this other person was a harsh marker (although quite fair), and didn't butter up her comments with compliments. if she thought your essay was crap, she would put lines through it etc..she was also a grammar nazi.
there were plenty o'tears when we got the marks back :S