As with the SAT, use Official ACT Test material only for practice tests, which are essential to prepare well for the ACT.

• The Official ACT Prep Guide 2022-2023 — I have a previous edition. This one contains 7 real tests. 
• 88 Official PDF Practice ACT Tests (FREE)

ACT Test Prep Book Recommendations:

• The Master Key to ACT Science — If you have trouble with the ACT Science Section, and you are committed to taking this test (versus the SAT, which does not have a Science Section), then this is the book for you. In addition to pointing out patterns, the book includes helpful in-depth explanations for the Science Sections of 5 real ACTs, which you can download from the McElroy Tutoring website.