ACT Science Study Guide

ACT says the Science section measures the interpretation, analysis, evaluation, reasoning and problem-solving skills required in the natural sciences. It presents several scientific scenarios, each followed by multiple-choice questions, drawn from biology, chemistry, Earth and space sciences (such as geology, astronomy and meteorology) and physics. Advanced knowledge is not required, though some questions need background from introductory science courses.

Optional, and Outside the Composite

• On national test dates, you choose whether to take Science. On state and district testing, the state or district decides.
• If you take it, Science comes after Reading.
• Your Composite is the average of English, Math and Reading only. Science cannot raise or lower it.
• Taking Science adds a Science score (1 to 36) and a STEM score, which combines Science and Math. ACT sends both on all your reports.
• The ACT Superscore Composite excludes Science, but the report still shows your highest Science and STEM scores.

The overall ACT guide covers whether to take it. This guide is about scoring well if you do.

The Numbers

40 questions in 40 minutes, of which 34 are scored. In ACT's 2025/2026 Practice Test 1, the questions are spread across seven passages of five to seven questions each. That is roughly five and a half minutes per passage. Calculators are not permitted, so any math is estimation, ratios or simple arithmetic.

In that practice test's conversion table, 34 correct is a 36, 32 is a 34, 30 is a 32, 25 is a 27 and 20 is a 23. Conversions vary by form.

Reporting Categories

Category	Share	What it asks
Interpretation of Data	38 to 50%	Analyze tables, graphs and diagrams: trends, translating tables into graphs, interpolation, extrapolation, mathematical reasoning
Scientific Investigation	18 to 32%	Experimental tools, procedures and design (controls and variables); compare, extend and modify experiments
Evaluation of Scientific Arguments and Models with Evidence	24 to 38%	Judge the validity of information; decide which explanation new findings support

The Three Passage Formats

Format	Share	What it presents
Data Representation	26 to 32%	Graphs and tables like those in science journals and textbooks
Research Summaries	50 to 56%	One or more related experiments and their results
Conflicting Viewpoints	18 to 21%	Two or more explanations of the same phenomenon that are inconsistent with one another

Research Summaries are about half the section. Experimental design is the single most valuable skill to practice.

A Four-Step Routine for Every Figure

1. Title and labels. What does the figure show, and under what conditions?
2. Axes and units. Which variable is on each axis? Is the scale even, or does it jump (1, 10, 100)? Are units in grams or kilograms, seconds or minutes?
3. Key or legend. Which line, bar or symbol is which group?
4. Trend. As the variable on the x-axis increases, does the other increase, decrease, peak, or level off?

The Skills Questions Test

• Reading a value: go up from the x-axis to the line, then across to the y-axis. Use your pencil or cursor as a straight edge.
• Interpolation: estimating a value between two data points. Assume the trend continues smoothly between them.
• Extrapolation: estimating beyond the data. Continue the trend in the same direction and at about the same rate.
• Relationships: a direct relationship means both variables rise together; an inverse relationship means one rises as the other falls.
• Translating: choosing the graph that matches a table. Check the direction of the trend first, then a single data point.
• Combining figures: some questions need a value from one figure to use in another. Note the shared variable that links them.

Worked Example: Interpolation

A table gives the speed of sound in air: 331 m/s at 0 °C, 343 m/s at 20 °C, and 355 m/s at 40 °C. What is the speed most likely to be at 30 °C?

• The speed rises by 12 m/s for every 20 °C, a steady trend.
• 30 °C is halfway between 20 °C and 40 °C, so the speed is about halfway between 343 and 355 m/s.
• About 349 m/s. No calculator needed.

If the question asked about 60 °C, you would extrapolate: another 20 °C adds about 12 m/s, giving about 367 m/s.

ACT advises you to consider each experiment's design, including the controls and variables, because questions are likely to address it. Before the questions, answer these for each experiment:

• What was changed on purpose? That is the independent variable.
• What was measured? That is the dependent variable.
• What was kept the same? Those are the controlled variables.
• Is there a baseline group with none of the treatment? That is the control.
• How does Experiment 2 differ from Experiment 1? Usually one thing changes. Name it.

Common Question Types

• Design: "Which variable was held constant?" or "What was the dependent variable?"
• Results: "Based on Experiment 1, which sample had the greatest...?" Go straight to the data.
• Predictions: "If an additional trial were run at..., the result would most likely be..." Use the trend.
• Supporting a claim: "A student claimed that... Do the results support this claim?" Answer the yes or no from the data, then choose the reason that cites the right data.
• Modifying the experiment: how to test a new question, which usually means changing one variable and holding the rest constant.

Worked Example: Reading a Design

A student placed equal amounts of yeast and sugar water in four flasks kept at 15, 25, 35 and 45 °C and measured the volume of gas produced in 30 minutes.

• Independent variable: temperature.
• Dependent variable: gas volume in 30 minutes.
• Controlled variables: amount of yeast, amount and concentration of sugar water, time.
• A follow-up that tests sugar concentration must keep the temperature the same and vary only the concentration.

These passages present explanations that disagree because they rest on different premises or incomplete data. The questions are less about graphs and more about reading carefully. ACT suggests noting a summary of each viewpoint.

1. Read the introduction to learn the phenomenon and what is agreed.
2. Write one line per viewpoint: the cause or mechanism it proposes.
3. Note agreement and disagreement. Viewpoints often share some points; questions ask which ones agree.
4. For new evidence questions, ask which viewpoint the evidence supports or weakens.

Common Question Types

• "Which of Students 1 and 2, if either, would agree that...?" Check each viewpoint separately. "Both" and "neither" are real options.
• "How does Scientist 2's explanation differ from Scientist 1's?" Choose the actual point of difference.
• "Which finding would most weaken Hypothesis 3?" Find what contradicts its key claim.

Do not judge which view is true. Questions ask what each viewpoint claims and what the evidence implies for it, not which one you believe.

Math You Should Be Able to Do by Hand

• Ratios and proportions: if 2 g dissolves in 50 mL, about 6 g dissolves in 150 mL.
• Percent and fractions: 15 out of 60 is 25%.
• Averages of two or three values.
• Rounding and estimating: choices are usually far enough apart that a close estimate decides.
• Using a given equation: if the passage gives a formula, substitute the values.

Pacing

• About five and a half minutes per passage across seven passages. Check the clock after each one.
• Answer the quick, single-figure questions first within a passage.
• Skim long procedures; return when a question needs the detail.
• Guess and move on if a question takes over a minute and a half. There is no guessing penalty.