I need to get a new prep book (that I'll actually use) for the February ACT. What's the difference between Barron's ACT and Barron's ACT 36?
The main difference between the two books is that Barron's regular ACT prep book is for general study, whereas Barron's ACT 36 is for students aiming to get a perfect score on the ACT. As we discuss in this article, the Barron's guides are extremely comprehensive when it comes to content, but tend to have questions that are more difficult than (or are difficult in different ways from) real ACT questions. So while both of the Barron's books are good if you really need to teach yourself subject content and make sure you don't miss anything, they also might also be a little overwhelming.
I encountered this myself when I was studying for a different test, the Psychology GRE Subject Test. I ended up using the Barron's book primarily for learning content I hadn't covered in my classes, but using another book for practice questions.
If you're not sure if you'll need an ACT prep book to learn test content vs just getting a book with practice questions, a good place to start is by taking a full-length, practice ACT. You may discover that what you mostly need is practice with the test, in which case there are several free, publicly available official ACT tests you can download and you won't need to purchase either of the Barron's books. On the other hand, if you find that there are certain content areas you're really struggling with (like coordinate geometry), you might want to consider purchasing either the general Barron's ACT (if you're aiming for a score in the 24-27 range) or the Barron's 36 (if you're aiming for a 36 and are currently already scoring above a 27).
Before purchasing any review book, however, I highly recommend taking a look over our content-focused articles on ACT Math, Reading, English, Science, and Writing. They're absolutely free and contain high quality explanations of different content areas within the ACT. And of course, if you really want to zoom in on your weak spots, the PrepScholar paid ACT prep program might be worth looking into.