everyone has different test versions, so for me, I can only speak for MY particular dat version
I only did the biology, GC, Orgo, and math on the free ADA DAT.
Biology of the real dat was a little harder I felt... not much harder, like 1 point difference (like the difference between a 20 and 21 score)
General chemis of the real dat was about the same difficulty as the practice
Orgo, oh boy, I felt like my DAT's orgo was ALOT harder than the free ADA test. I remember when I did the free ADA orgo, I didn't miss any questions, it was very easy and basic, which equates to a score of about 28-30. But on my DAT, I got a 21 on my orgo, there was some reactions there that I have NEVER seen before.
Finally the MATH of the free sample test was easier I felt than the DAT's math.....