<p>I guess some of the practice tests are harder than others. Like, I heard that Barron's practice tests are harder than the other ones.
As for tips, I recommend using Barron's ACT. Some people that use said it was difficult, but if you master it, then you'll do better.</p>
<p>It's very true that some of the practice tests are harder than others, especially when they come from different test-prep companies. With that said, the most accurate way to track your improvement would be to stick to one test-prep company at a time. For example, if you take a Kaplan practice ACT, try to take another Kaplan one to get a better sense of how much you are improving. Switching around does not allow you to compare as easily.</p>