We run a very successful test prep company and highly recommend The Real ACT Prep Guide to students. It is important to note that the ACT is one of the most predictable tests ever created. This test always tests the same skills--in the same amounts!--on each section of the test. For example, the English test will ALWAYS have 10 questions testing punctuation, 12 questions testing grammar, 18 questions testing sentence structure, etc. And within those categories, the same skills are always tested. This predictability can be found in all sections of the test. The math section will ALWAYS have 14 plane geometry questions, 4 trig questions, etc.
Why am I blabbering on about this? Since the ACT is so predictable, the best way to prep for the test is to take official ACTs. The same question types just repeat and repeat. With enough practice, you'll know exactly what to expect on test day. And no, the fake Princeton Review and Kaplan ACT practice tests just don't cut it. (Just check out all those Amazon reviews for those books. Sadly, they are filled with comments like, "The tests in this book were nothing like the real thing. Not a good thing to find out on test day." Oy.)
This book is the only one out there offering real ACT tests. You need this book!
There are several problems with this book, however:
1) The Real Guide doesn't give you a "big picture" view of the skills you need to improve. Let's say you answer a test question incorrectly and review the answers and explanations. Hopefully, you won't get a similar question wrong next time. But you don't necessarily have a "macro" sense of the topics you need to review.
2) Even if you realize what skills you need to improve, the Real ACT Prep Guide doesn't really review any skills tested on the ACT. Don't remember how to calculate the distance formula? Forgot what subject-verb agreement is? You're stuck.
3) The Real ACT Prep Guide doesn't offer practice problems (besides for the 3 included tests). We often find that students who are most successful practice with hundreds of practice problems before test day (particularly those practice problems that focus on their weak areas).
4) The Real ACT Prep Guide doesn't offer "sneaky" strategies. After all, this would be a conflict of interest for the ACT folks.
As a result, you need more for good ACT prep. In our program, we use Boost Your Score! The Unofficial Software Guide to the Real ACT along with this book, since it analyzes student performance on the real ACT tests in the book and then provides practice problems and strategies to boost weak areas. We have actually turned out two perfect scorers using the software in combination with The Real ACT Guide.
Other good products we have used include Princeton Review's 1,296 ACT Practice Questions (College Test Preparation) or the Kaplan or Princeton books when they are used just for strategy, but not for the practice tests.