Test prep is stressful no doubt, and some people need help in getting their minds around all the information they're expected to learn fro the test.
The relationship between a student and a tutor can take multiple tones. Personally I don't like the "traditional relationship" where a student stays politely quiet, and waits for the tutor to "divulge his wisdom". I prefer to treat students, even those much younger than myself as peers when working with them. The respect this shows for the time the student is investing in me helps them become much more engaged in what I'm saying, retain more of our lesson, and want to come back and work with me again.
My most memorable experience was when one particular student felt completely insecure about taking the SAT. By focusing on one section at a time, we made slight gains each week. This student was starting out in quite a low range, but slowly her diagnostic tests were improving. The actual test was even better, the student scored in the 700's on all sections of the exam.
You can never tell from the initial diagnosis how a student will score, but by showing a student proper respect, they'll want to be engaged in their own learning. Out of that will come something extrodinary.