The science section of the ACT is really measuring how well you can read charts and graphs and extract information, so studying random science texts won't be as effective as prep books that teach test-taking strategies (how to approach the problems, how to eliminate wrong answers right away, etc.) Any ACT prep book would work for that, although DS found the Official ACT Prep Guide to be the most useful.
ETA: Another factor that can significantly help with science scores is lots of timed practice tests under realistic conditions. Since science is the last section on the test, stamina can be a significant issue. I know that the first time DS took the ACT, he was just completely fried by the time he got to science and he didn't come close to finishing it (he was having to read and reread everything multiple times, and just really struggled to stay focused). After a couple of months of focused test prep, including several timed practice tests, he raised his science score to a 33.
Edited by Corraleno, 01 January 2018 - 09:24 PM.