I've been working with kids preparing for the ACT/SAT for over 10 years. Through this time, I've come to some conclusions. I hope you find them of interest.
First, these standardized tests are mainly aimed at testing a student's problem solving ability. Consequently, most of the test prep courses aim at that skill. Learn the best methods to solve a problem and you'll make the best score on the test that you can. What this also says is that if your capability is to make a 25, no amount of test preparation is going to allow you to make a 30. I had a student who made a 27 on the ACT, which was near her top capability. After two more test preparation classes and taking the test two more times, she made a 27.
Second, there are some students who get themselves worked up and nervous about tests. Consequently they do not to their best. Many of the ACT/SAT preparation classes work on this issue by giving the student a test taking plan that gives them confidence. A plan also removes much of the stress that comes with a timed test in which most students can't actually work all the problems. Put simply, most students should not walk into the test expecting to work all the problems. By removing this expectation, we relieve the pressure and give the student a method to answer all the question but only work the ones they need to in order to achieve their desired scores.
Third, these tests are long. No class in high school gives students three and four hour tests. Mental fatigue is a huge factor for everyone in the room. I can't overemphasize the need for students to be well rested and alert both mentally and physically. Walking into a test with 4 hours sleep and no breakfast isn't the best way to do it. Most courses recommend a good night's sleep, a good breakfast, and a short amount of exercise just before the test.
Finally, I'll address parental expectations. I've had excellent students make a 19 on the ACT. I've had poor students make a 28. I know which of these two I'd rather have in class. Give me someone who works hard every time. So parents, realistically measure your children's test scores against their demonstrated abilities. Realize also that grades, classes taken, and extracurricular activities also play important parts in the college acceptance process.
Closing political comments: Equal opportunity and equality are two very different things. And never trust the government to give you what you should be earning for yourself.