I took my first ACT practice test last Saturday, and I've been going through my answers and trying to learn from my mistakes. I noticed that the SAT provides an Answer and Explanations booklet for practice tests, but it seems as though the ACT does not. Are there explanations for ACT practice test questions somewhere?
The Real ACT Prep Guide, 3rd Edition, published by ACT, Inc., does include answer explanations for all the practice tests in the book. It's important to note, however, that this book was (as of December 2015) last updated in 2011, and so doesn't include some of the changes to the Science section or the new ACT essay. The explanations you'll find in there for the most part, though, are helpful.
Unfortunately, the free official ACT practice tests available online don't have answer explanations for the multiple choice questions. Some of these practice tests do have sample essays for the essay questions, but with the exception of the 2015-2016 Preparing for the ACT booklet (which doesn't have any sample essays), the essay prompts are all in the old format and therefore the sample essays are probably not super helpful.
One other place to look for answer explanations is the PrepScholar Blog. Several of the guides to specific skill types have walkthroughs for answering questions. For instance, all the ACT Reading skill guides (Little Picture/Detail, Big Picture, Function and Development, Inference, and Vocab-in-Context) take at least one sample question and explain how to crack it. Be sure to check out our other ultimate guides to ACT English, Math, and Science for links to other skills guides with other explanations!