Control of Variables Strategy – an important gap in your science curriculum?

Two children are on the field arguing – Nike trainers are faster than Adidas – No they aren’t.

You propose an investigation. A race around the field, one wearing Adidas and one wearing Nike. Best shoes win.

What is wrong with this investigation?

If you’ve said something like, “But the runners aren’t equal – you don’t know if it’s the shoe or the runner,” then you are using the Control of Variables Strategy (CVS). It’s an key tool in science reasoning. There is quite a lot of research showing that it is important – not just as ‘how science works’ knowledge, but because understanding CVS accelerates science learning. 

The paper I’m basing this post on is ‘The Importance of Being Able to Deal With Variables in Learning Science,’ by Bryant, Nunes, Hillier, Gilroy & Barros (2013).

The authors used data from the Bath longitudinal study. They constructed a basic model for comparing KS2 science SATs results to KS3 science SATs results – a simple formula. Then they attempted to improve the formula by adding in other factors. 

The relationship between KS2 SATs and KS3 SATs was fairly good, but the relationship between a combination of KS2 SATs and an additional CVS assessment was even better. The implication is that knowing the CVS strategy at the end of year 6 led to better assessment outcomes in year 9. 

It’s only an implication – this paper shows that the Y6 pupils who understood and could use CVS went on to outperform peers who scored the same in their KS2 SATs 3 years later. But the paper does not show that a CVS intervention in KS2 would cause improved outcomes at secondary school. It’s correlation only.

How Should We Teach the Control of Variables Strategy?

We know the answer to this question. Two teaching strategies work, according to a meta study by Schwichowa, Croker, Zimmerman, Höfflera and Härtiga (here):

  1. Model the CVS strategy to pupils – show them how to use the CVS and explain what you are doing as you go. 
  2. Use Cognitive Conflict – give them examples of experiments which don’t control the variables and ask them to point out the problems. E.g. if you were comparing solubility of different solutes, use different volumes of water at different temperatures and stir one but not the other – ask them to point out the errors. 

At Paradigm Trust, where I work, we are introducing explicit CVS instruction at KS2 in our science curriculum this term. We are trialling the strategies, training colleagues and developing our knowledge rich curriculum ready for a September launch.

Further reading on the power of direct instruction on teaching CVS even to younger pupils:  Klahr and Nigram, 2004 (here).

Enquiry methods also work: Schalk, Schwyz, Edelsbrunner, Deiglmayr, Schumacher 2016: MINT Longitudinal Study.

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