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ACT Science reporting category

ACT Scientific Investigation Practice

Scientific Investigation questions ask how an experiment was set up: what was changed, what was measured, what was held constant, and what would happen if the procedure changed. According to ACT, this category makes up 18–32% of scored science questions. The procedure matters as much as the results table.

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18–32% of scored Science questions3 original questionsInstant answer checks

At a glance

Scientific Investigation on the ACT: the key numbers

Section and category facts from ACT.org, checked October 9, 2026. Time per question is ACT's section time divided by its question count.
SectionACT Science: 40 questions in 40 minutes
Scored questions34 scored, 6 field test
Reporting categoryScientific Investigation
Share of scored questions18–32%, according to ACT
Average time per questionAbout 60 seconds
Counts toward the CompositeNo, Science is optional
Practice on this page3 original questions: Easy, Medium, Hard

What this tests

What does ACT Scientific Investigation test?

Practice questions

Practice ACT Scientific Investigation questions

Pick an answer to check it. Each question has one correct choice.

Question 1 of 3Easy

A student tested how light affects the growth of radish seedlings. She planted 20 radish seeds in each of four identical trays filled with the same potting soil.

Each tray was placed under an identical lamp at a distance of 20 cm, 40 cm, 60 cm, or 80 cm. Every tray received 50 mL of water each day, and the room was kept at 22°C. After 10 days, she measured every seedling and calculated the average height for each tray.

Which of the following was the independent variable in this experiment?
Show answer and explanation
Correct answerD. The distance between the lamp and the tray

How to solve it

  1. The independent variable is the condition the experimenter changes on purpose from one group to the next.
  2. Only the lamp distance differed among the trays: 20, 40, 60, or 80 cm.
  3. So the distance between the lamp and the tray is the independent variable, choice D.
Why the other choices miss
A and B were the same for every tray (50 mL per day and 22°C), so they are controlled variables. C is the outcome the student measured after 10 days, so it is the dependent variable.
Question 2 of 3Medium

Students studied how fast antacid tablets react with water. Every tablet had a mass of 1.0 g, and every trial used 200 mL of water in identical beakers. Students timed each trial from when the tablet entered the water until bubbling stopped.

Experiment 1: A whole tablet was dropped into water at 10°C, 20°C, 30°C, or 40°C.

Experiment 2: A tablet was left whole or broken into 2, 4, or 8 pieces, and all the pieces were dropped into water at 20°C.

Results of Experiments 1 and 2
ExperimentWater temperature (°C)Number of piecesReaction time (s)
110192
120161
130144
140132
220161
220252
220443
220835
Suppose Experiment 2 were repeated with the water at 40°C instead of 20°C. Compared with the reaction times in Experiment 2, the new reaction times would most likely be:
Show answer and explanation
Correct answerA. shorter for every number of pieces.

How to solve it

  1. Experiment 1 shows the effect of temperature: each warmer trial was faster, and a whole tablet took 61 s at 20°C but only 32 s at 40°C.
  2. The repeated Experiment 2 keeps each number of pieces the same and changes only the temperature, from 20°C to 40°C.
  3. Warmer water sped up the reaction in every Experiment 1 trial, so each new time should be shorter: choice A.
Why the other choices miss
B reverses the temperature effect shown in Experiment 1. C and D both fail for a whole tablet, which Experiment 1 already measured at 40°C: its time fell from 61 s to 32 s, not stayed the same or rose.
Question 3 of 3Hard

Researchers built six sloped trays of soil to study runoff, the rainwater that flows off the surface instead of soaking in. Each tray was 1 m long and filled to the same depth. Water was sprinkled evenly over each tray for 5 minutes, and the runoff was collected in a trough at the lower end.

The researchers varied the soil type, the slope of the tray, and the volume of water poured. The table shows the conditions and results.

Runoff from six soil trays
TrialSoil typeSlope (°)Water poured (mL)Runoff collected (mL)
1Sand1050040
2Sand2050075
3Clay10500210
4Clay201,000560
5Loam10500120
6Sand201,000190
The researchers want to find out how soil type alone affects runoff. Which three trials should they compare?
Show answer and explanation
Correct answerB. Trials 1, 3, and 5

How to solve it

  1. To isolate soil type, the trials must use different soils while the slope and the water poured stay the same.
  2. Trials 1, 3, and 5 use sand, clay, and loam, and all three have a 10° slope with 500 mL poured.
  3. Any difference in their runoff (40, 210, and 120 mL) can then be credited to soil type, so the answer is B.
Why the other choices miss
A uses sand in all three trials, so soil type never changes. C uses only sand and clay, and Trial 2 got 500 mL of water while Trials 4 and 6 got 1,000 mL. D repeats clay, and Trial 4 also changes the slope and the water poured.

Avoid these traps

What mistakes do students make on Scientific Investigation?

Mixing up the variables

The independent variable is what the experimenter sets; the dependent variable is what gets measured. Swapping them flips answers about cause and effect.

Fix: Ask what the researcher chose before each trial started. That is the independent variable.

Missing a second change

Two trials can look like a fair comparison but differ in two conditions, so neither condition can be credited for the difference in results.

Fix: Compare every column for the trials in question, not just the one the question names.

Skipping the procedure

Answers about controls and design often depend on a setup detail, such as a fixed temperature or volume, that never appears in the results table.

Fix: Mark each condition in the procedure as changed or held constant before reading the results.

Study method

How should you practice ACT Scientific Investigation?

  1. Before looking at results, list what the experimenters changed, what they measured, and what they kept the same.
  2. When there are several experiments, write one line per experiment naming the variable it changed.
  3. For pairs or sets of trials, check every condition; a fair comparison differs in only one.
  4. For predictions, find the existing results closest to the new condition and follow their pattern.
  5. Practice experiment-design questions in Dolphin, and write the changed variable for each one before you answer.
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FAQ

Questions about ACT Scientific Investigation

What is the difference between an independent and a dependent variable?

The independent variable is the condition the experimenter changes on purpose, such as water temperature. The dependent variable is the result measured in response, such as reaction time. Controlled variables are the conditions kept the same so the comparison is fair.

How much of ACT Science is Scientific Investigation?

According to ACT, Scientific Investigation makes up 18–32% of scored science questions. ACT lists Interpretation of Data at 38–50% and Evaluation of Models and Results at 24–38%.

What science subjects does ACT Science cover?

ACT says the science section measures interpretation, analysis, reasoning, and problem-solving in biology, chemistry, and Earth and space sciences. Investigation questions in any of those subjects use the same skills: identify the variables, check the controls, and compare the procedures.

Is ACT Science optional?

Yes. Science is an optional add-on to the ACT, and it does not affect the Composite score. Students who take it also receive a STEM score, the average of their math and science scores. Check whether the colleges or programs you are applying to ask for it.

How do I find the control in an experiment?

Look for the trial or group that sets a baseline, such as plants given no fertilizer or water at room temperature. Then check that the other trials match it in every condition except the one being tested.

Related practice

ACT Interpretation of Data PracticeACT Evaluation of Models and Results PracticeACT Statistics & Probability PracticeAll ACT Science practiceACT English practiceACT Math practiceACT Reading practiceDolphin ACT prepSAT vs ACTCollege ACT score ranges

Sources

Where these facts come from

ACT facts checked . Every practice question on this page is original Dolphin practice written to match one ACT reporting category. None is a released ACT item.

ACT® is a trademark registered by ACT, Inc., which is not affiliated with, and does not endorse, Dolphin.