Diagnostic and formative information
In the original trials, even when they could identify a variable that affected how far the toys would travel, few students at Year 4 wrote a sensible explanation. Some examples of responses from the original task, both with and without an explanation, are shown in the table below.

Identify a variable only

NOTE: The data are from the original trialled task Ideas about forces and energy.

Students at this level were most likely to write explanations using intuitive ideas based on previous experiences and observations rather than science concepts, and this is appropriate at this age. Some are beginning to use scientific vocabulary, but have an unscientific understanding of the word. Some examples are:

• Because the carpet is bumpy so it has a reaction and it stops.
• Because the carpet will have hairs sticking out all over the place which will slow down the force.
• If it goes too steep it will flip at the bottom.
• Because the higher the car is the further it will go. It will happen as the force of height slows it down.
• The slope will make it easier for the car to come down.
• It is a flat surface so it can't go unless you push it.
• If they are on a slope it goes down but when there is a flat surface the car doesn't go anywhere.

Next steps
Students need lots of experiences observing what happens in different circumstances. The focus at this level should, for most students, be building up these experiences, and using their personal theories to develop simple explanations using their terminology rather than worrying too much about abstract ideas about forces. Ask questions that encourage them to think further about what they have noticed and what they might want to try out next.

Get students to test their predictions. At this level they are likely to need support to include fair testing principles. Isolate each variable students suggest and help them plan a test. The table below provides some examples. (Different groups could do different tests according to their initial ideas.)

Refer also to Further Resources, especially Figure it Out: Forces.

Students could then use their results to provide evidence that their predictions were correct or not. Encourage them to extend their explanations to identifying not just the variable (for example, the floor surface), but also why that has an effect (e.g., the bumps in the carpet slow the car down, a steeper slope makes a car go down faster so it takes longer to slow down and goes further). When they are doing this they are starting to use their science understandings, even if these are based only on what they have noticed, to support their explanations.

Next steps

Class and/or group discussions are a good way to develop skills in developing explanations. Give students practice in backing up their predictions with reasons, initially orally. A structure that scaffolds them to do this can be helpful, e.g. I think ……… because ………
Once they are used to doing this during discussions they can then be encouraged to record their explanations in written form. Predict, Observe Explain (POE) is another more structured strategy to encourage students to explain their ideas. It could be used to attend more closely to the variables. Examples of questions that would be suitable for a POE are:

• Will a toy car go further on wood or carpet?
• Will the four wheel drive or the fire engine go further?
• Will a toy car go further on a steep or flatter ramp?

If more appropriate for your students, their ideas could be gathered orally. Encourage students to critique and build on others' explanations, again providing reasons for their ideas. Possible teaching points to focus on include:

• Do students consider other information as it becomes available and revise their explanation?
• Do students ask questions for clarification?