ACT Science is mostly reading and data interpretation, but a handful of questions per test assume basic science knowledge that the passage does not fully explain—think simple biology, chemistry, physics, or math ideas you would recognize from intro classes. That share is small, so do not turn Science prep into a content memorization project. For the big picture, read is ACT Science mostly reading.
What kind of outside knowledge shows up
When prior knowledge matters, it is usually at a very basic level: states of matter, what a control group is, simple genetics vocabulary, density, or reading a formula the passage mentions but does not define. You will not need AP-level facts, and you will never need to recall an entire unit from chemistry class.
When outside knowledge helps
Background science can speed you up when a question uses a familiar term without defining it, or when a graph axis label assumes you know what a variable means. If you recognize the concept instantly, use it—but only as a shortcut to understanding what the passage is already showing you.
When outside knowledge hurts
The trap is importing what you learned in class when the passage says something different. ACT Science is designed so that every scored answer is supported by the figures or text in front of you. If your memory conflicts with the data, trust the passage. That rule matters most on experimental design questions; see ACT Science experimental design questions.
Do not overstudy content
Spending weeks reviewing biology textbooks will not move your score much. The fastest gains come from reading graphs faster, tracking variables, and running a repeatable passage method. Build that with the best ACT Science strategy.
Trust the passage first, always
On every question, start with what the passage gives you. Use outside knowledge only to decode a term or save ten seconds—not to override what you see on the page. If you cannot point to evidence in the passage or figures, your answer is probably wrong.
What to do if you hit a knowledge gap
When a term is unfamiliar, read the surrounding sentences for context. Science passages almost always define or illustrate what you need if you look. If you are still stuck, pick the answer that best fits the data and move on. One mystery word should not cost you a minute.
Chasing a top score
At the highest levels, every lost question counts, so knowing basic science vocabulary can be the tiebreaker on one or two items per test. But even students aiming for a 36 should spend most of their Science prep on data skills, not content review. For that level of detail, see how to get a 36 on ACT Science.
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This article offers general ACT prep guidance. The ACT can change from year to year, including its format, scoring, policies, test dates, and fees, so always confirm the latest details on the official ACT website at act.org before you make decisions. ACT® is a registered trademark of ACT, Inc. thirty-six is not affiliated with, endorsed by, or sponsored by ACT.