It’s a good idea to do some prep before the ACT, even if it’s last-minute.
Science: For students familiar with the SAT, the ACT’s Science section may come as a big surprise on test day. While the Science section is not terribly difficult, most students mismanage time the first time they try one. (To help with time management, skim the passages (one at a time) and quickly get to the related questions. The questions will only require that you refer back to, and fully understand, specific sections of the text. Thus, reading the entire passage in detail is not the best use of the time allotted.)
Math: The ACT math section is much more straightforward than SAT math. Unlike the SAT, however, the ACT covers more advanced topics like trigonometry. (Practicing before test day is a great way to refresh your memory on concepts you may have forgotten over the years and to learn essential topics that you may not have covered yet in school.)
Reading: The ACT Reading section does not include sentence completion questions like the SAT. The ACT Reading section includes only a series of passages with linked questions. Unlike the SAT passage based questions, however, some ACT questions go beyond reading comprehension. They require the test-taker to make decisions regarding the structure or function of specified portions of the text provided. (It’s a really good idea to expose your mind to these types of questions before test day.)
English: In concept, the ACT English section is much like the SAT Writing section. (Because the format is different, however, it would behoove you to take a practice test before you sit for a real ACT.)
Good luck on Saturday to all taking the ACT!