As far as I know,There are two general reasons for the students afraid of examinations.In the one hand is didn't understand the knowledge what they learn in class , on the other hand is the personal psychological .
I have different suggestions for this different problems. first If you are afraid of the examinations because of you didn't grasp the knowledge. I suggest to begin review the knowledge one month before the exam . Remember that all knowledge is not afraid of the examinations will be forgotten.
And if you are afraid of examinations because of psychological reasons. I suggest go to bed early the night before the exam. I think the day of the test you can have a relaxed feel .This will allow you better play in the exam.
I hope my advice can help them , that's all thank you