I don't know about the ACT, but my impression of the SAT is in line with what HK's dd reports. Looking at SAT prep books, the SAT math is fairly easy theoretically and computationally, but the problems often involve a series of calculations and a twist or trick at the end. So, for example, perhaps the hard part of the question is that you have to factor a quadratic equation and it takes awhile to do so, but the question asked in the end is not the value of x or y but is (due to a twist in the question) actually 1/2 x. Maybe that's not a good example, but what I'm getting at is that I and my dc's tend to see a math question and jump to what's hard and what's (usually) important, which in this case would be doing the factoring right. We might process it so quickly that we don't read the extra sentence at the end saying that the value requested is 1/2x. That's why the SAT gives an advantage to preparation: you will have seen that trick a million times and will watch for it.
I know nothing about these tests, but if the SAT has these kinds of "tricks", then it is prudent to at least spend some time to be prepared for them.
