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Experimental Design

Teach Students the Design of Experiments

By Oliver Smith

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Get your students to learn like scientists.


Science is a mixture of historically accumulated knowledge and skills. These practical skills range from problem solving to data analysis; they are wide reaching and can be applied a lot outside the classroom. The teaching of these skills is a very important part of science education, but is often overlooked by the teaching of the content. As science educators, we have all seen the benefits of students doing practical work on engagement and understanding. However with the time pressures placed on the curriculum, the time needed for students to develop these investigative skills can get squeezed out. Too often we give students a ‘recipe’ to follow which doesn’t allow students to take ownership of their practical work. Students from a very young age start to think about the world around them. They ask questions then use observations and evidence to answer them. Students tend to have intelligent, interesting and testable questions that they love to ask. We as educators should be working towards encouraging these questions and in turn, nurturing this natural curiosity in the world around them.

Teaching the design of experiments and letting students develop their own questions and hypotheses takes time. These materials have been created to scaffold and structure the process to allow teachers to focus on improving the key ideas in experimental design. Allowing students to ask their own questions, write their own hypotheses, plan and carry out their own investigations is a valuable experience for your students. This will lead to students having more ownership of their work. When students carry out the experimental method for their own questions, they reflect on how scientists have historically come to understand how the universe works.





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Experimental Design Process

1. Question

This is a key part of the scientific method and the experimental design. Students really enjoy coming up with questions. Formulating questions is a deep and meaningful activity that can really give students ownership over their work. A great way of getting students to think of visualize their questions is using a mind map storyboard.

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Ask students to think of any questions they want to answer about the universe or get them to think about questions they have about a particular topic. All questions are good questions, but some are easier to test that others.


2. Hypothesis

A hypothesis can also be known as an educated guess. A hypothesis should be a statement that can be tested scientifically. At the end of the experiment, look back to see whether the conclusion supports the hypothesis or not. Forming good hypotheses can be challenging for students to grasp. It is important to remember that the hypothesis is not a question, it is a testable statement.

One way of forming a hypothesis is to form it as an “if... then...” statement. This certainly isn't the only or best way to form a hypothesis, but can be a very easy formula for students to use when first starting out. An “if... then...” statement requires students to identify the variables first, and that may change the order in which they complete the stages of the visual organizer.

After identifying the variables, the hypothesis then takes the form if [change in independent variable], then [change in dependent variable]. For example, if an experiment were looking for the effect of caffeine on reaction time, the independent variable would be amount of caffeine and the dependent variable would be reaction time. The “if, then” hypothesis could be: If you increase the amount of caffeine taken, then the reaction time will decrease.


3. Explanation of Hypothesis

What led you to this hypothesis? What is the scientific background behind your hypothesis? Depending on age and ability, students use their prior knowledge to explain why they have chosen their hypotheses, or alternatively, research using books or the internet. This could also be a good time to discuss with students what a reliable source is.


4. Prediction

The prediction is slightly different to the hypothesis. A hypothesis is a testable statement, whereas the prediction is more specific to the experiment. To take the example of the discovery of the structure of DNA, the hypothesis was that DNA has a helical structure. The prediction was that the X-ray diffraction pattern of DNA would be an X shape.


5. Identification of Variables

Below is an example of a Discussion Storyboard that can be used to get your students talking about variables in experimental design.

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The three types of variables you will need to discuss with your students are dependent, independent, and controlled variables. To keep this simple you could refer to these as "what you are going to keep the same", "what you are going to change", and "what you are going to measure". With more able students you should encourage them to use the correct vocabulary.

Dependent variables are what is measured or observed by the scientist. These measurements will often be repeated as more repeated measurements makes your data more reliable.

The independent variable is a variable that scientists decide to change to see what effect it has on the dependent variable. Only one is chosen because it would be difficult to figure out which variable is causing any change you observe.

Controlled variables are quantities or factors that scientists want to remain the same throughout the experiment. They are controlled to remain constant, so as to not affect the dependent variable. Controlling these allows scientists to see how the independent variable affects the dependent variable.

Use this example below in your lessons, or delete the answers and set it as an activity for students to complete on Storyboard That.

How temperature affects the amount of sugar able to be dissolved in water
Independent VariableWater Temperature
(Range 5 different samples at 10°C, 20°C, 30°C, 40°C and 50°C)
Dependent VariableThe amount of sugar that can be dissolved in the water, measured in teaspoons.
Controlled Variables
  • Volume of water (500 mL - measured using a graduated cylinder)
  • Type of water (get the water from the same tap)
  • Whether the water is stirred or not
  • Type of sugar
  • Grain size of the sugar

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6. Risk Assessment

Ultimately this must be signed off on by a responsible adult, but it is important to get students to think about how they keep themselves safe. In this part, students should identify potential risks and then explain how they are going to minimize risk. An activity to help students develop these skills is to get them to identify and manage risks in different situations. Using the storyboard below, you could get students to complete the second column of the T-chart by saying, "What is risk?", then explaining how they could manage that risk. This storyboard could also be projected for a class discussion.

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7. Materials

In this section, students will list the materials they need for the experiments, including any safety equipment that they have highlighted as needing in the risk assessment section. This is a great part to talk to students about choosing tools that are suitable for the job. You are going to use a different tool to measure the width of a hair than to measure the width of a football field!


8. General Plan and Diagram

It is important to talk to students about reproducibility. They should write a procedure that would allow their experimental method to be reproduced easily by another scientist. The easiest and most concise way for students to do this is by making a numbered list of instructions. A useful activity here could be getting students to explain how to make a cup of tea or a sandwich. Act out the process, pointing out any steps they’ve missed.

For English Language Learners and students who struggle with written English, students can describe the steps in their experiment visually using Storyboard That.

Not every experiment will need a diagram, but some plans will be greatly improved by including one. Have students focus on producing clear and easy-to-understand diagrams.


9. Carry Out Experiment

Students then follow their plan and carry out the experiment. It is important that students collect their results in a meaningful and easy-to-understand way. Data is often recorded in a table, but could also be done with photographs, drawings of observations, or a combination. It may be helpful to have students write down any difficulties and problems they had when carrying out the experiment. This could help later with evaluating their experimental method.


It is important to mention that any experiments students design should be thoroughly risk-assessed by the responsible adult before letting any students carry out their practical work.


After completing the procedure of the experiment, students analyze the data, draw conclusions, and then share their results. Depending on the student level, this might be a formal lab report, graphs, class discussion, or other.


Completed Examples





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Resources and Examples

Using visual organizers is an effective way to get your students working as scientists in the classroom.

There are many ways you could choose to use these investigation planning tools to scaffold and structure students' work while they are working as scientists. Students can complete the planning on Storyboard That using the text boxes and diagrams, or you could print them off and have students complete them by hand. Another great way to use them is to project the planning sheet onto an interactive whiteboard and work through how to complete the planning materials as a group. You could also project it onto a screen and have students write their answers on sticky notes and put their ideas in the correct section of the planning document.

With very young learners you can still start to get them thinking as scientists! They have loads of questions about the world around them and you can start to make a note of these in a mind map. Sometimes you can even start to ‘investigate’ these questions through play.

The foundation resource is intended for elementary students or students who need more support. It is designed to follow exactly the same process as the higher resources, but made slightly easier. The key difference between the two resources are the details that students are required to think about and the technical vocabulary used. For example, it is important that students identify variables when they are designing their investigations. In the higher version, students not only have to identify the variables, but make other comments, such as how they are going to measure the dependent variable. As well as the difference in scaffolding between the two levels of resources, you may want to further differentiate by how the learners are supported by teachers and assistants in the room.

Students could also be encouraged to make their experimental plan easier to understand by using graphics, and this could also be used to support ELLs.





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Assessment

Students need to be assessed on their Science inquiry skills alongside the assessment of their knowledge. Not only will that let students focus on developing their skills, but will also allow them to use their assessment information formatively to help them improve their science skills. Using Quick Rubric, a quick and easy assessment framework can be created and shared with students so they know how to succeed at every stage. As well as providing formative assessment which will drive learning, this can also be used to assess student work at the end of an investigation and set targets for when they next attempt to plan their own investigation. The rubrics have been written in a way to allow students to access them easily. This way they can be shared with students as they are working through the planning process so students know what a good experimental design looks like.




Printable Resources

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