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Practicals, demos and knowledge: CogSciSci responds

This post launches a new series of blogs, where we ask teachers from the CogSciSci community to respond to a specific article, blog post or educational event. We hope you find it interesting and if you would like to contribute or suggest a piece of reading for us to discuss please be in touch with

Here at CogSciSci we are big fans of Doug Lemov’s Teach Like a Champion. For those who don’t know much about it, Lemov spent years observing expert teachers and painstakingly recording and classifying the practices which he saw most often into an incredibly useful book. He recently wrote a blog on his website about how his daughter had a great time in her science class building paper rockets, but learnt nothing about forces, aerodynamics or sophisticated observation.

Below, teachers from the CogSciSci community share their thoughts on the relationship between student knowledge and the impact of demonstrations and practical work.

Rebecca Flint:

Imagine this: 30 students sat in front of me, all buzzy from the practical we had just completed. I pose the question “So what did that tell us about immobilised enzymes?”


”okay, what did we observe happening, Josh?”

….deepening silence.

I could feel the deflation, I could see the lack of eye contact and then it hit me: it didn’t work. They had no idea what they were supposed to observe. They couldn’t make any links and to top it off it was an observed lesson. This occurred about 7 years ago and is my first conscious and vivid realisation (I probably had others but have blocked the trauma) that engagement does not equal learning. Learners cannot make connections if the don’t know what to connect. They can’t articulate knowledge that they don’t have. So now when I do a practical I always ask myself “how will they know what they are looking for?”, “what will they get out of it?”. If the answer isn’t the demonstration or confirmation of knowledge then is there any point?

Bob Pritchard:

Doug’s blog post certainly chimes with my own experiences. In the first half of my career my first thoughts when planning lessons were “how can engage them? What demos and experiments can I do?” There’s an element of this embedded in school Science culture; the majority of school open evenings are all about the whiz bang of Science lessons. “Are we doing a practical?” and “can we blow something up” are questions pupils often ask (repeatedly) as they enter Science labs.

Don’t get me wrong; engagement IS important. The awe and wonder aspect of Science is pretty unique. But it shouldn’t come at the cost of learning. A number of us have already written about our misadventures with “engaging activities” (you can find my contribution here).

I would generally agree with Doug’s comment that “the value of hands-on in other words correlates to how much students know when they engage in it.” I now normally get pupils to complete practical investigations AFTER they’ve been taught the theory for that very reason; they then have the knowledge to understand what they’re doing and what to look for. It also avoids experimental results accidentally creating misconceptions (I used to have a number of pupils convinced that white
was a better radiator than black due to some dodgy black/white tin experiments).

There are, however, some exceptions (aren’t there always?). Sometimes a demo or experiment can demolish a pupil’s preconceptions with devastating effect, for example the coin and feather falling in a vacuum when teaching gravity. You can then teach the correct science and revisit the demo in light of their new understanding.

Niki Kaiser

I was chatting about this yesterday during a break at ResearchEd, in the context of Science lessons, and the idea that you might take a familiar example from life (for example, a microwave oven) and then dissect how and why it works. There are so many ideas you can talk about here: heat and temperature, radiation, the electromagnetic spectrum. Depending on prior knowledge, you would pick which aspects to highlight, and which to leave for a later date. In my opinion, practical activities and demonstrations, can play this role. 

Look at this! A moment ago, the bottom of this beaker was wet. Now, that water has frozen, and it’s stuck fast to the block it’s standing on! Let’s unpick why this is.

In his book on Rosenshine’s principles, Tom Sherrington talks about how, when you’re presenting new material by breaking it into small steps, you might ‘build up’ (keeping a goal in mind, like baking a cake) or you might ‘zoom in’ (giving context, exploring language and discussing the era for a line in a poem). Again, I see a role here for practical work.

Thinking about how the iron appeared to go red when we put it in the blue copper sulphate solution, let’s think about what that red coating might be, and where it came from.

I wouldn’t, of course, do this type of activity out of nowhere. Before introducing displacement of copper ions from solution (as above), I would ensure my students knew things like the colours of solid copper and iron, what a solution is, what happens when ionic compounds dissolve in water and a range of other things. But I might do a practical activity involving displacement reactions, before I actually teach my class the specific theory behind them.

Practical work is, in my opinion, an integral part of Science education. I’m a flautist, and you could tell me everything there is to know about how a flute works; about the history of music; about dynamics and tone. But unless I pick up the flute and play, I’m not a flautist. I could tell my students all about colour changes in solution, coatings on metals, how ions are displaced from solution and a range of (fairly abstract) ideas. But, from experience, I think it helps my students if they can root this new knowledge in a recent, concrete example. 

Maybe this is what Doug’s daughter’s teacher was hoping to achieve: you can talk about air resistance and aerodynamics, but it’s also powerful to experience it, and develop that tacit, contextual knowledge through experience, and deepen your understanding of it later. 

I do think there’s a place for capturing attention, inspiring curiosity and triggering a sense of awe and wonder in Science lessons, and I wouldn’t want to lose this. I could tell you all about the wonder of Mahler’s fifth symphony, which I played in a recent concert. I could give you the score, show you the chorale section, describe the heart-stopping horn solo, even sing it to you! But I think you’d be able to appreciate it all much better, if you’d sat in the concert and listened to it first. If you had experienced it, and been moved to tears with us, before you started to look at the mechanics of it, you’d understand them much better.

Having said that, I do know that practical work can be done badly. I can list a number of ways I’ve used it badly during my teaching career: to keep classes busy; to keep classes happy (“are we doing a practical today, miss?”); with classes that lacked sufficient prior knowledge to really understand what was happening; in an overly complex way, so that students were concentrating so hard on the ‘recipe’ that they didn’t have time and space to think about  why they were doing it. And that’s just a few of them! 

I should also say that I don’t know the context of Doug’s daughter’s school, or even have a really deep knowledge of her education system. I also don’t know how old she is, or what she had (or hadn’t) learned before she built rockets.

But practical work can (and should, in my opinion) be at the heart of what we do. I could talk about acids reacting with carbonates in a really detailed and compelling way. But if you’ve not experienced that jump-out-of-your-seat moment when a sealed plastic container containing baking powder and vinegar explodes in front of you, I think you’ve missed out!


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