TL;DR:
Identify the variables and units before anything else. Most wrong answers come from reading the wrong column or the wrong unit.
Find the trend in each table or graph, then check the numbers that the question points to.
Do not read the whole passage first. Read the labels, then the question, then only the data the question needs.
ACT science is less about knowing science facts and more about reading data quickly and accurately. A typical data passage gives you a table or a graph, a short description of an experiment, and several questions. The students who do well treat the figure as the passage and read the text only when a question sends them there.
Start with the labels, not the story
Before reading any sentence of the description, look at the table headings or the graph's axes. Write down three things: what was changed on purpose (the independent variable), what was measured as the result (the dependent variable), and the units of each. The description will tell you the same things in words, but the labels are faster and harder to misread.
Units matter because questions often compare two columns that are measured differently. A column in minutes next to a column in seconds is an easy trap. Circle the unit in every heading you will use.
Find the trend before the detail
Once you know the variables, look at the overall shape. Does the measured value go up, go down, level off or jump? A trend is the answer to most questions about a passage, and the detail numbers are there to confirm it or to answer a specific question.
A quick way to find the trend in a table is to compare the first and last rows, then check one or two rows in the middle. In a graph, look at where the line starts, where it ends and whether it climbs or falls between them.
Worked example: one data representation passage
Here is a short data passage written for this article. A student heats three samples of water and records their temperatures. The table below shows two of them.
Time (minutes) | Sample A temperature (°C) | Sample B temperature (°C) |
|---|---|---|
0 | 20 | 20 |
2 | 26 | 22 |
4 | 32 | 24 |
6 | 38 | 26 |
8 | 44 | 28 |
Variables and units: time is the independent variable, measured in minutes. Temperature is the dependent variable, measured in °C. There are two samples, A and B.
Trend: both temperatures rise over time. Sample A rises faster than sample B, because its values climb by larger steps.
Rate for sample A: the change is 44 − 20 = 24 °C over 8 − 0 = 8 minutes, so the rate is 24 ÷ 8 = 3 °C per minute.
Rate for sample B: the change is 28 − 20 = 8 °C over 8 minutes, so the rate is 8 ÷ 8 = 1 °C per minute.
Compare: 3 ÷ 1 = 3, so sample A warms three times as fast as sample B on this data.
Check each step against the table. Sample A goes from 20 to 26 in 2 minutes, which is 6 °C in 2 minutes, or 3 °C per minute. Sample B goes from 20 to 22 in the same 2 minutes, which is 2 °C, or 1 °C per minute. The short-interval checks agree with the rates found over the full eight minutes above.
Now suppose a question asks, at 4 minutes, which sample is warmer and by how much. Read the row for time 4 only: 32 °C for A and 24 °C for B. The difference is 32 − 24 = 8 °C. You never needed the rest of the passage.
When to read the words
Some questions are about the design of the experiment, such as why a control was used or what a researcher changed. Those answers are in the description. Read the sentence that the question points to, and only that. Reading the whole description first costs time and rarely helps with the data questions.
Some questions ask you to predict what would happen under a new condition. Use the trend you found and say what it implies, but don't add outside facts that the passage doesn't mention.
Mistakes to avoid
Reading the whole passage before the figure. Look at the labels and the question first.
Comparing values with different units, or reading a row for the wrong time.
Calling a trend from one pair of points. Check at least three points before you describe a pattern.
Choosing an answer that is true in science but not shown in the data. Stay with what the passage shows.
Your plan for this week
Time yourself on one data passage: Use a practice passage from the official ACT materials. Note the time you spend before you look at the first question.
Label before you read: Write the independent variable, the dependent variable and both units in the margin, before the first question.
Answer from the figure: For each question, write the rows, columns or axis points you used before you pick an answer.
Review the misses: For each wrong answer, note whether it came from a wrong label, a wrong unit or a wrong row.
Most passages reward the same habits: labels first, trend second, the specific numbers last. Practice that order on ten passages, and the method will feel automatic.
Frequently asked questions
Do I need to know the science topic already?
Some background helps, but these passages usually give you what you need. The skill is reading the data accurately.
What if a graph has two lines that cross?
Note where they cross, then read each line on either side of the crossing. Questions often ask which one is higher at a given time.
Should I skip a hard passage?
Check the labels and the first question. If it still doesn't come together, move on and come back with the time you have left.
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