My dd11 just took the ACT, and I had similar questions. I took the advice of the other posters and just had my daughter work through the practice test so she was familiar with the format. She took the English and reading practice tests without issue on a timed basis, and we went over the answers together so she could see the reasoning. She freaked out a bit over the math and science, so instead of timing her on them we just went through the test together and I walked her through some of the questions so she had a better understanding of what they were asking. Once she realized the science was really more of a reading test and she had to infer the data rather than knowing it she was more confident.
I did not want to expose her to new concepts just for the test because that would have put more pressure on her to try to get things right. We went into it just wanting to know where she was currently to help plan for our first foray into homeschooling.
My dd does not like taking tests, so we did just enough to make sure she knew what to expect. She had no problems with the actual test and actually enjoyed meeting some of the other young kids there taking it through NUMATS. Although after we got the results this week she informed me she will not be taking it again until absolutely necessary ;-)
