High-stakes only means that if one passes the exam, one is "through the gate" and if one fails the exam, one must re-take the exam, at expense of time and money, as well as brain power.
That means that a student preparing for any high-stakes test must study diligently ahead of time to get prepared to take the test. That might include going to a tutor for help, but it cannot eliminate the need for the test-taking student to do his own "due diligence" and study on his own so that he knows the material.
It is the student who must sit for the exam, not the tutor. So while a tutor may be helpful, yes, certainly, but the student cannot leave it 100% in the hands of the tutor to provide all the information needed to pass the test. The student must put forth his own individual effort to learn the types of problems that will be tested, and how to arrive at their answers, how to check his work to be sure it is correct, and how to evaluate his final answer to make sure it is reasonable.
Obtaining a Study Guide and reading through it and working the problems in it is an excellent way to prepare for any high-stakes test. Order a Study Guide online, have it shipped to you, then sit down every day for a period of time such as 45 minutes to read the Study Guide very carefully, understand what it says, work through sample problems, take practice tests, and after that is done, you would be ready to sit for the exam.