The Rank given for our mock test days is for the whole country so your student will be compared to many hundreds (minimum of around 500, often more depending on the test) of students.
We give local averages, high and low scores in the results email.
Because the number of students who take tests online is much higher, the number of people who take the same test more than once is negligible. I did the stats once to remove 2nd attempts and it had practically no effect on the ranks.