The ACT's Science section is optional and scored separately. It doesn't count toward your composite score at all: since September 2025, the composite is the average of English, Math and Reading only. If you take Science, you also receive a STEM score, the average of your Math and Science scores. So is it worth the extra 40 questions and 40 minutes? It depends on where you're applying and what the section actually tests.
What the Science section actually tests
Despite the name, ACT Science is not primarily a test of memorized biology, chemistry, or physics content. It's a test of reading and reasoning about scientific data -- interpreting graphs, tables, and experimental setups, comparing conflicting viewpoints or hypotheses, and drawing conclusions from data presented directly on the page. Most of the information you need to answer a question is right there in front of you; the skill being tested is extracting and reasoning about it quickly, similar in spirit to the Reading section but applied to scientific data instead of prose.
Related: What to Expect on the ACT: Format, Scoring, and How to Prepare
Who actually requires it
Whether you need a Science score depends entirely on the specific schools you're applying to. Some colleges, particularly for competitive STEM programs, may specifically ask for it or weigh it more heavily; many others don't require it at all and only look at your three-section composite. Check the specific testing requirements published by each school on your list -- don't assume it's required (or unnecessary) based on general reputation, since policies vary school to school and can change from year to year.
How to prepare, if you decide to take it
Because the section rewards a specific data-reading skill rather than subject-matter recall, the most effective prep is practicing with real, full-length Science sections under timed conditions -- not reviewing biology or chemistry textbooks. Get comfortable quickly identifying what a graph or table is actually showing, noticing when two passages present conflicting viewpoints or data sets, and answering directly from what's given rather than pulling in outside science knowledge you might have learned in class. Since the section moves fast -- roughly 60 seconds per question -- timed, full-section practice matters more here than almost anywhere else on the ACT.
The bottom line
If none of your target schools ask for a Science score, there's no real cost to skipping the section -- you save 40 minutes and can focus your prep entirely on the three required sections. If even one school on your list wants it, or you're unsure whether your list might change, taking it (and budgeting real, dedicated prep time for it specifically) is the safer choice, since you can't add a Science score to an ACT report retroactively without retesting.