Teaching by Contrast

This is my new thing. Teaching by contrast. My department know this is my new thing because I keep going on about it. A couple of them have tried it out too. They put up with a lot. Bless them!

Teaching by contrast works well when you have underlying procedural knowledge to teach across a few different contexts which you can explicitly compare to each other; I recently blogged about planning this approach (described by Mark Enser as Interweaving) here. This blog is a follow up and also offers a few more examples of how the approach could be implemented as well as reflecting on the initial impact on pupils.

Opportunities

This approach seems to suit certain areas of science better than others. So far I have used it when teaching about the different groups of the periodic table in chemistry, transport in organisms in biology and I can think of several more areas especially in biology where this would work too. Physics is proving a little more tricky, for example I can’t work out how I could use it for Newton’s laws but it did work well for displacement-time and velocity-time graphs. I blogged recently about using dual coding when teaching about diffusion and active transport and the approach I took here was also an example of teaching by contrast.

Following this we looked at where the processes occur in different parts of the body with pupils responding using whiteboards to questions such as:

• If oxygen diffuses from the alveoli to the blood, where will the highest concentration of oxygen be?
• If there is a higher concentration of carbon dioxide in the blood, where will it move to and by what process?
• If there is a higher concentration of glucose in the blood but we need more from the intestines, what process will it move in by?
• (Having drawn arrows showing oxygen diffusion from alveoli to blood and blood to cells) Can you place the blood, cells and alveoli in order from highest to lowest oxygen concentration?

The powerpoint slide used animation to introduce just the alveoli and bloodstream first (to avoid cognitive overload) and we focused on exchange of substances there. Then I asked why we exchanged these substances, where does the carbon dioxide come from to reactivate memories of aerobic respiration. Next the small intestine appears and I ask why to elicit thoughts of glucose which we then focus on. Then we can think about where these substances are going, how they get there via the bloodstream and why they move into cells. This enabled several links to prior knowledge and pushed for depth of understanding as to why we need to transport substances around our bodies.

The Old Ways

Having worked in a number of science departments there was always a pretty standard approach to teaching topics. The first biology topic, for example, is likely to be sequenced something like…

• Lesson 1 – Animal cells
• Lesson 2 – Plant cells
• Lesson 3 – Bacterial cells

… and so on. This would involve pupils learning to identify the parts within animal cells and learning the functions of the parts in lesson 1, then the parts of plant cells and their functions in lesson 2, then repeating these in lesson 3 for bacterial cells. Due to the fact that all of these cell types share some organelles does create some repetition of describing the functions and there may some “higher level” questioning which gets pupils to compare. But this isn’t the focus. It feels added on.

The lessons tend to be set up for the intended learning to be:

• Identify organelles
• Describe functions

For many pupils this may not be adequately challenging. You could tag a lesson on to the end where the focus is purely comparison but it may be more beneficial to build this skill in throughout.

I’ve tried to go a bit “Efrat Furst” in the diagrams below. Hopefully they illustrate the development of schema reasonably well!

With Contrast Comes Challenge

By changing the design of the scheme of work, bringing in clear opportunities to contrast the different types of cell, the intrinsic level of challenge can be increased. For example:

Lesson 1 – Identifying organelles

• Identify organelles in animal, plant and bacterial cells
• Compare the structure of animal, plant and bacterial cells

Lesson 2/3 – Describing the function of organelles

• Describe the function of organelles in animal, plant and bacterial cells
• Compare the functions of animal, plant and bacterial cells.

Within each of these phases of learning there is an increased level of challenge. The first lesson could be seen as relatively easy as they are just identifying structures found within cells but with the focus then being on using the acquired knowledge to compare the cells pupils are able to rehearse the declarative knowledge in a more challenging context. It also provides an opportunity for some extended writing which can be clearly modeled beforehand.

“Both animal and plant cells have a nucleus and mitochondria whereas bacterial cells do not. The plant cells and bacterial cells both have a cell wall however animal cells only have a cell membrane”

“Only plant cells can photosynthesise because they have chloroplasts; animal cells and bacterial cells are unable to make their own food.”

What are the benefits?

The main benefit which I have perceived, especially when teaching about the reactivity in group 1 versus group 7 of the periodic table is the opportunity to repeat the deep, structural procedural knowledge which governs a greater process.

Having had a lesson where the reactions of group 1 and group 7 were observed in order to be able to describe the trends down the group and producing some comparative writing we could move on to the explanation. The reactivity is governed by the atomic radius and amount of shielding by electrons and to what extent they affect the electrostatic attraction between the nucleus and outer shell electrons. By comparing and explaining the reactivity trend in both group 1 and 7 we were able to show that these aspects must be described each time. The contrast came from the different intents of metals v non-metals (either gaining or losing electrons). I used cognitive supports to enable pupils to tackle the more challenging work like the one shown below.

By pushing students to perform more effortful thinking across a range of different procedures (e.g. identifying then comparing, describing then comparing) pupils’ knowledge will become more durable and flexible. They have thought about the content in several different ways within a phase of learning. Due to the temporal separation of lessons the fact that you are building schema within the same contexts each lesson leads to the spacing effect being an added benefit; something which is lost with a more linear approach. You could also argue (probably successfully!) that due to working in this comparative manner you are introducing desirable difficulties which will also lead to better retention and transfer of knowledge.

What does this look like in the classroom? (Cheers Carl and Robin!)

Teaching by contrast leads to pupils struggling. To me this is a good thing. Pupils have to think harder about the content they are engaging with and will require support at times. As a teacher you have to be extremely responsive in your differentiation (by support obviously) and the checking of the understanding of all students is paramount to success. Questioning is king. Modelling and feedback are vital along with plenty of opportunities to practise knowledge in a variety of ways.

I have used this approach to teach a chemistry unit to a triple science group, who I feel have benefited but are untested as yet, and a colleague (Miss Emily Balmforth – a genuinely good egg) has taught her middle set (mixture of middle and low prior attainment students) using the lessons I planned. She has taught the whole topic, revised and tested the class. Her feedback is detailed below.

• The usually higher and middle attaining pupils within the class have experienced a positive impact as a result of teaching by contrast. The test scores of the usually lower attaining students haven’t been adversely affected but haven’t shown improvement either.
• It’s harder to teach but it clearly benefits students in terms of the higher demand required as they have had to think much harder in lessons; this has then resulted in higher test scores.
• The quality of their answers has also been much better for example they’ve written “as you go down the group the reactivity increases” whereas they’d usually just write “it increases”.

As yet I haven’t attempted teaching by contrast with the lowest prior attaining sets where, in my setting, you find higher numbers of EAL students but this opportunity will arise when we change timetable in July. I expect there may be some adjustments needed; possibly a streamlining of the curriculum and we spiral the content required for the foundation paper and repeat it a few times. I will be playing that one by ear!

The Results are in!

Throughout the teaching of the OCR Chemistry C4 topic I have utilised several techniques as well as aiming to teach by contrast. I’ve used live drawing on several occasions, dual coded, used retrieval questions at the start of each lesson, integrated instructions for one of the practical lessons and have gone full Rosenshine on the model, guide practice and independent practice over and over again.

With this class in the past I have taught them how to revise, using practice questions and flashcards, in lesson time but in this topic I simply provided them with several sets of Qs and a stack of flashcards for them to make and use over the spring bank holiday. The pupils completed the test at the end of the first week back, after several pupils in the class were off school celebrating Eid, giving a two week gap between the final lesson and the test. Plenty of time for some forgetting to take place!

The results for the last few tests this group have completed are shown in the table below. There is a caveat that this is a shared class so not all topics are taught by me so obviously ideal comparison is impossible.

The results from the C4 topic are as follows:

• Average Score 32/50
• Range 14 – 42 (the 14 is an anomaly, the next lowest score was 22)

Removing the anomalous child’s score actually lifts the average over 33/50. This is a relatively huge shift in attainment as according to our (approximated) gradings it moves the average grade from 6 to 7.

The previous year’s group I taught this topic to, using a non-contrasting style, were a similar ability range set and their average point score was 26/50 ranging from 16 to 43 marks respectively. In conclusion it would appear that evidence-informed teaching, with a little extra creativity, has been pretty darn effective in this case. Long may it continue!

As always please do comment, share and challenge. This feels like an exciting and effective approach to delivering science and if any of you can share useful knowledge from your own experiences that would be gratefully received!

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