I drink a big glass of grape juice and eat a cinnamon & sugar bagel that morning. I've never really had a problem with anxiety during the actual test, so I've never had a problem with scores. I usually get anxious the day before a test, and to calm down I'll pace and repeat whatever pops into my head. The only times I've stressed over a test were in math class because I am notoriously bad about checking my work, or showing my work, which causes problems with the teacher, who, for some reason, needs me to show her how to find the answer to a problem she's already solved. (And heaven help us all if my way is somehow different than hers.)
What kind of tests are you stressed about? All of them? The standardized ones? The in-class ones? The AP tests? Math tests? Oral exams? (Okay, I ALWAYS get anxious before, during, and after one of these.)
I also found that having a tape ball to play with helped reduce any anxiety I felt during a test.
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Superman wears Jack Bauer pajamas.