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Enabling students to design and carry out experimental inquiries is an important aspect of learning about scientific processes. The first step in this process is the generation of an experimental or testable question.

What makes a testable question different from other types of scientific questions?

Testable questions are ones which can be answered through experimental inquiry and observation of the natural world. Questions that cannot be answered by direct observation or by evidence gathered through experimental inquiries (i.e., “why…” questions), are not testable questions. Questions which require an opinion, or could be answered differently by different people, are also not testable questions. It is important to note that not all scientific questions can be answered through experimental inquiries. For example, many discoveries in astronomy, such as the irregularities of the orbits of Uranus and Neptune, only came about through careful observation.

Testable Questions

A testable question is a question that can be answered using scientific methods such as:

  • Research
  • Field Study
  • Experimentation

First and foremost, testable questions require defining of the variables of the experimental inquiry. This means they include what will be varied (changed) and what the impact that changing the variable is expected to have. Testable questions are about changing one variable to see what the effect is on another variable.

For more about variables, see:

Identifying Variables

Testable questions often begin with question starters such as How…? What…? If ...? Does…? and have a style such as:

  • If we change fill in the blank_______ how does it affect fill in the blank_______?
  • What happens to fill in the blank_____ if we change fill in the blank_____?
  • How does changing fill in the blank______ affect fill in the blank______?
  • How does fill in the blank______ affect fill in the blank________?

You may already use SMART goals in the classroom, but the concept of SMART can also be used when developing testable questions for experimentation in the classroom.

S = Specific

The more specific the question, the easier it will be to design and implement a scientific inquiry. For example, “How does soil affect germination?” could be made more specific by changing the question to “How does the temperature of soil affect the number of seeds that germinate?”

M = Measurable

When developing testable questions, students should be thinking about what measurements they will need to make and what data they will need to collect. Keeping this in mind can help students refine and clarify their questions. For example, in the more specific question above, students would be measuring the temperature of soil (using a thermometer) and collecting data about the germination (keeping track of when the seeds sprout).

A = Attainable

When brainstorming testable questions, students could be thinking “Could this experiment be done with the time and materials we have?” If not, what would be needed? Is it practical to do in the classroom?

R = Relevant

Ideally, testable questions will lead to answers that are of value to the students and will further their understanding of science concepts. Encouraging students to come up with their own testable questions can motivate students to find answers.

T = Timely

Similar to the A for Attainable, students could be thinking “Do we have enough time to do this experiment?” For example, if the investigation is about how the amount of water affects the size of tomatoes on their tomato plants, this will take months to complete and may in fact go beyond the end of the school year.

How does Tomatosphere™ model the asking of a testable question?

In the Seed Investigation, the inquiry question is provided to the students:

How does exposure to the space environment or space-like conditions affect the number of tomato seeds that germinate?

Is this a testable question? Yes!

  • The question follows a testable question style (e.g., How does changing fill in the blank___ affect fill in the blank___?)
    In the Seed Investigation, we are asking how does changing the location of seeds prior to planting (i.e., the space environment) affect how many of them will grow (i.e., the germination rate).
  • The question is specific (is clear what is being changed).
    The testable question of the Seed Investigation is about changing the type of seeds (seeds which have been in space or have been treated to a ‘space-like’ environment vs. non-treated seeds)
  • The question can be answered through observation and measurements.
    In the Seed Investigation, students will be observing and measuring germination rate; in other words, how many of the seeds germinate.

Guided Practice

Have students read the following questions and determine if the questions are testable or not and why.

  1. What makes plants grow best?
  2. How does soil affect the growth of tomato plants?
  3. How does the duration of light exposure affect the surface area of tomato plant leaves?

Answers

Not a testable question. Why is this not a testable question?

  • incorrect Does not follow the testable question style “How does changing fill in the blank___ affect fill in the blank___?”
  • incorrect Too broad to be easily testable in a single experiment. What would be changed? Light? Water? Soil? Something else?
  • incorrect No clear measurement involved. What does “best” mean? – Fastest? Tallest? Most biomass?

Have students work on changing this non-testable question into a testable question.

(E.g., How does changing the amount of water affect the germination of the number of tomato seeds that germinate?; How does blue light affect the height of tomato plants?)

Not a testable question. Why is this not a testable question?

  • correct Does follow the testable question style “How does changing fill in the blank___ affect fill in the blank___?”
  • incorrect Too broad to be easily testable in a single experiment. What aspect of the soil would be changed? Nutrients? Water? Temperature?
  • correct Question could be answered through measurements (i.e., growth could be measured)

Have students work on changing this non-testable question into a testable question.

(E.g., How does changing the type of soil affect the height of tomato plants?; How does changing the temperature of soil affect the number of tomato seeds that germinate?)

Testable question. Why is this a testable question?

  • correct Does follow the testable question pattern “How does changing fill in the blank___ affect fill in the blank___?”
  • correct Question could be answered through measurements (i.e., growth could be measured).
  • correct Duration of light can be controlled. Surface area of leaves can be measured

Additional Resources