Practice test scores not accurate?

I advise and tutor students for the praxis core. We use Khan Academy as an aid and guide to help students prepare. 

I would like to know how the scores are calculated for the practice test? I had two students take a practice test and showed them with a reading score of 164 and a math score of 158, which would both be passing in our state. When they showed me a picture of their raw score and both students scored 60%. I am not sure how that raw score got translated to such a high passing score. This gave my students a false sense of confidence and they did not head my warnings that they needed to study more. They both failed the test (148 for both reading and math). 

 I have generally heard you want to be 70-80% to have a good chance and 80% or above you should be fine. 

How accurate are the Khan Praxis core practice test scores? If they are not accurate they should just report raw scores.