At a high level, each set of mock tests, i.e., 1 and 2, 3 and 4, 5 and 6, shares the same question base, and each can be taken twice. Since 1 and 2 are free, most candidates end up attempting them, so they tend to be better calibrated in terms of difficulty. All of them use the same algorithm as the real test, except for experimental questions, so you won’t see much difference otherwise. There’s also a general perception that the later tests are relatively more difficult, but it could simply be because those questions are less widely circulated. You’re less likely to see them discussed on forums compared to the free ones, so that might be one reason behind that belief but it’s hard to definitively justify any real difference otherwise.
Nkathiyawadi
GMAC provide GMAT Official Mock Tests 1 to 6, in which mock tests 1 & 2 are free. What is the difference among all these 1 to 6 mock tests ?