Yes, if you are one of those people that know you need to prepare for the SAT or ACT but just can’t get motivated to do the work by your self. If that is you, take a general test prep class to understand what the test is all about and take some practice tests.
No, if you are motivated to do well, are willing to study by your self and take practice tests to figure out what weaknesses you have. Then, knowing your weaknesses, you are able to figure out how to improve those weaknesses on your own.
No, if you are already scoring well on the tests. And by well I mean above a 750 on each section of the SAT or a 34 and above on the ACT.
Maybe, if you are that self motivated person who has done all of the practice tests but are still struggling to understand certain concepts. If that is you, consider hiring a tutor to work with you on those specific areas.
No, if you are just blindly taking a test prep class because everyone is doing so. Following the crowd is usually not very helpful when it comes to college admissions.
For most of the students that I deal with, general test prep is not much help. The studies that have been done show an improvement of only 30 points on the SAT and less than 1 point on the ACT after general test prep classes.
If you have the motivation to do so, and I hope you do, take some practice tests to see which test is the better test for you. Once you have determined that, start taking practice tests. Pay particular attention to the questions you get wrong. If you can figure out the concepts you are struggling with then you know where you need to focus your energy.
If you are still struggling with the concepts, hire a good tutor. If you want or need test prep, that is the way to go. It probably won’t cost any more money than a general prep class and is usually much more effective.