Awwh don't let them bring you down. Instead use them to fuel you further - prove them wrong or try your damnest to do that anyway.
I always run a commentary in my head when things like this happen... 'here she goes again and can anyone guess what she'll say...of course its the same old thing. Deary she should just record herself. Would save a lot of energy. Clearly she's run out of real interesting things to talk about' etc. Might as well mock it all and make a joke of it (though do try not to snigger in their face). [Of course it is no laughing matter really, but whatever helps goes right?]
Maybe print some motivational quotes and stick them around your room etc. I know someone who did that and whenever they felt they couldn't do it, would read that.
Ask teachers etc for extra help if you need and never feel embarrassed to ask even the simplest of stuff. It will show that you are trying and are determined.
Some people find that upbeat music helps them. Not my thing but might be yours.
Give yourself little treats every now and then to keep you motivated.
Just try your best and keep strong girl!!
Oh one more thing... make your own cheerleader style song for example:
You go (insert name), you can do it
You are the best, you can beat the test
(Okay that was a rubbish attempt on my part but I used to do this myself. If you wanted could add your own moves to it too)
Good luck. Wish you all the best! Hope you get your AA!!