1. Exploring students’ prior knowledge
Students have their own ideas about a topic and an effective teacher takes account of these ideas when teaching. So a good way to start teaching any topic is to find out what your students already know about the topic. You may be surprised about what they have learnt from newspapers, adults, peers, older brothers and sisters and observations. Often their ideas are not the same as the scientific ideas we want them to understand. Why do you think that is the case?
At primary school, students may have learnt that matter can be divided into solids, liquids and gases. They will not necessarily remember all the details, but they will certainly not be ‘empty vessels’. If teachers assume that they need to start from the beginning then students easily get bored and there is a danger that they will keep any misconceptions they have.
Activity 1 is designed to consolidate and extend their understanding and for you to develop your ability to probe understanding through questioning. It is important to make sure that your questions challenge your students. Resource 1 reminds you about the different types of questions that you should be asking. It is a good idea to plan the questions that you could ask before the lesson. Think about how you might respond to their answers. You could ask several students the same question then ask the students to select the best one. You could also ask a follow-up question: ‘Why do you think that?’
Resource 2 provides some background to the teaching activity described in Case study 1. The activities will help you to build on the knowledge and understanding that your students already have.
You start by revisiting ideas that they will have met in primary school, but then extend these to more substances, helping them to realise that lots of things around them are a mixture of a solid and a gas, or a solid and a liquid. For example, a sponge looks like a solid but doesn’t have all the properties of a solid.
Case study 1: Investigating a new substance
Mr Yaya planned a fun activity for his class (see Resource 2). When he was at college one of the lecturers showed him that if you mix corn starch and water in certain quantities they make a very peculiar substance. He went to an internet café and found a film on YouTube of someone walking on custard (a mixture of corn starch and water). Mr Yaya divided his class into groups and gave them a bowl of corn starch which they had to mix with water. He gave them 10 minutes to play with it. He then gathered them round the front and started asking them questions. He started with closed, easy questions based on their observations. What colour is the mixture? Does it smell? Then he asked some more open-ended questions. What have you discovered? Do you think it is a solid or a liquid? Why do you think it is a solid or liquid? He let several different students answer the same question. He asked them about particles. He found that several children remembered how the particles are arranged in a solid, but a lot were confused by liquids. He drew diagrams on the board and gave them another chance to experiment with the mixture. While they were working he asked them questions to make them think about whether it was a solid or a liquid and how the particles might be arranged. Finally he gathered them round the front and asked one group to argue in favour of it being a liquid and one to argue for it being a solid.
The students had a lot of fun and by the end, Mr. Yaya was confident that they remembered the properties of solids and liquids and how the particles were arranged in each one.
Activity 1: Using questioning effectively
You will need to collect a set of objects or pictures of objects that represent solids, liquids and gases. Some of them will be obvious, some will be more difficult to classify as they will be a mixture of a solid and a gas (e.g. a sponge) or a liquid and a gas (e.g. a picture of a cloud, bottle of fizzy drink) and some will be unusual (e.g. jelly or plasticine). Resource 3 has some suggestions. Before the lesson divide your objects (or pictures) into two groups – those that are obvious and those that are more complicated. Gather your class round the front. Ask easy closed questions that will help them remember the properties of solids, liquids and gases. Summarise the properties of solids, liquids and gases on the board. (You could ask one of the students to do this). If as a result of your questioning you find this is too easy for them, go straight on to the more difficult objects.
Good teachers will change their plan if necessary to stop the students getting bored. When you are confident that the properties of solids, liquids and gases are understood, introduce the second group of pictures or objects. Ask them to work in groups of four to discuss how the objects can be classified. Keep asking them why. Why can the sponge be compressed? Why does sand flow? Get each group to report back on one of the objects. Encourage the others to ask questions.