Working one-to-one with an experienced tutor often helps to substantially improve a student’s performance in exams by:

Helping to increase confidence and in turn decrease exam nerves.
Ensuring the student has a thorough knowledge and understanding of the syllabus.
Going through past-papers. This is essential and doing so with a tutor who not only knows the subject matter but all the tricks of the trade gives a student a real advantage.
Having someone to whom you can ask those questions that you have not perhaps had the time, opportunity or confidence to do so at school.