I assert that about 99% of students can benefit from preparation. Unless the student is in the top 1% on the ACT or SAT, he or she has room to improve.
In making your decision, look at the admission factors at the colleges your child is applying to and decide if a better score would make a difference with respect to admission or in the bid for a scholarship.
Look at where your child currently stands. How do their class rank and test scores compare with what it usually takes to gain admission to those colleges?
For example, say your child has an ACT score of 26 and is in the top 5% of their class, and you have determined that they have a very strong shot of being admitted. You have decided that they do not need a higher ACT score to get in, but you are not sure about scholarships.
Next, you call the school and find out that if your child raised their score to a 28, they would qualify for a $3000 annual scholarship. This is a situation where they stand to gain a lot from raising their score. $12,000 is on the line — getting a score of 28 will not be easy. It will take some work and I would advise that you locate the best preparatory program available to you and go for it.
Excerpt from The Parent's Guide to the SAT and ACT by James Pipkin
