No Guesswork. No Nonsense.

As a trainee, I was frequently told of the virtues of carrying out practicals in science lessons. These ‘investigations’ were touted as crucial tools for engaging pupils in science, allowing them to learn about new concepts through exploration, experimentation and enquiry. Rather than learning the underpinning knowledge first, I should create conditions for my pupils to discover scientific principles for themselves. My academic tutors and school mentors taught me that this approach was best because it simultaneously deepens pupils’ understanding and increases their engagement.

But the longer I teach, the more I realise that this approach simply does not work. Rather than deepening understanding and increasing engagement, putting experiments at the heart of the curriculum wastes time and reduces the amount of scientific knowledge they can acquire. Instead of learning about key scientific principles and learning them by heart, understanding their complexities and scope, pupils flap about with Bunsen burners and chemicals, guessing why things happen and never really getting to grips with the facts.

Without a firm understanding of important underpinning principles prior to beginning an experiment, pupils focus too heavily on the method rather than the actual science. For example, carrying out an experiment on thermal decomposition without much prior knowledge of the process would inevitably result in few tangible learning gains. Rather than observing (and crucially- understanding) the chemical changes during the complex process of thermal decomposition, pupils’ minds are more likely to be focused on whether they have pushed the rubber bung and delivery tube into the test tube properly. Whilst these things are important, and learning the method is one aspect of the process, pupils must first have a good knowledge of the chemical processes and changes happening if they are to truly appreciate what’s going on. If they are to remember these scientific concepts in the longer term, pupils first need to ensure that they know the content. Practicals provide an opportunity to see their knowledge in action, but they should not be used to learn the content in the first place.

Once pupils have learned the knowledge properly and have carried out the experiment, I then ask them to write up their findings. Below is one pupil’s report. It highlights the level of scientific knowledge they have gained throughout the process. The level of understanding is attributed to the knowledge first, experiment second model of instruction. Without a firm foundation, it is very difficult for pupils to gain a deep understanding of scientific principles.

The aim was to heat copper (II) carbonate to produce copper (II) oxide and carbon dioxide. This is known as thermal decomposition. We would first measure the copper carbonate using a special precise measuring scale. My partner and I had an initial mass of 23.3 grams for the copper carbonate. We then placed the test tube on a clamp which held it over a Bunsen burner with the collar (air hole) of the burner closed. We then held another test tube filled with three mL of limewater into the delivery tube. After a short time, we turned the collar of the Bunsen burner completely open. The limewater eventually turned cloudy. This was because the copper carbonate (CuCO₃) had decomposed into copper oxide (CuO) and carbon dioxide (CO₂). The carbon dioxide had moved into the limewater, causing it to become cloudy. We then measured the mass of the copper oxide. Our measurement of mass was the same as before, but that was because some of the limewater had condensed on the inside of the copper carbonate test tube, which had altered the mass of the test tube. There were also some chemical changes; the calcium carbonate had also lost two oxygen (O) atoms and one carbon (C) atom. This had formed CO₂, which had transferred into the limewater. If condensation had not occurred, the mass would have decreased because CO₂ molecules left the test tube by travelling through the delivery tube. The physical properties of the copper carbonate had also changed as it transferred into copper oxide; the solid had changed colour from a light green to a dark green and blackish colour. Our class knew all of this theory prior to the practical as we learned about the practical and were given a clear and detailed demonstration by Miss Dyer. We had a lot of knowledge about the practical beforehand so that pupils would be in a safe environment and able to focus on the science.