# Commentary

All the evidence suggests that when teachers think about the structure of their subject, they become better at creating the frameworks of understanding that are so important in subject teaching. It is clearly impossible for young people to carry in their heads the sort of framing that you, or a textbook writer, have after years of study. You need to be able to build such frameworks of understanding, as well as explaining the content of the subject. This means thinking carefully about the subcategories of information that will help students understand a big idea. For example, look at Big Idea 5 from the scientists’ list and the first elaboration of this idea:

> 5. The composition of the Earth and its atmosphere and the processes occurring within them shape the Earth’s surface and its climate

> Radiation from the Sun heats the Earth’s surface and causes convection currents in the air and oceans, creating climates. Below the surface heat from the Earth’s interior causes movement in the molten rock. This in turn leads to movement of the plates which form the Earth’s crust, creating volcanoes and earthquakes. The solid surface is constantly changing through the formation and weathering of rock.
> [88 words quoted.] (Harlen, W. (ed.), 2010, pp. 21–22)

The curriculum designers elaborated this even further by suggesting which concepts could most appropriately be taught at different ages. For example, for 5–11 years:

## For 5 –11 years:

There is air all around the Earth’s surface but there is less and less further away from the surface (higher in the sky). Weather is determined by the conditions and movement of the air. The temperature, pressure, direction, speed of movement and the amount of water vapour in the air combine to create the weather. Measuring these properties over time enables patterns to be found that can be used to predict the weather a short time ahead. Long-term patterns in the weather are referred to as the climate of different parts of the world.

Much of the solid surface of the Earth is covered by soil, which is a mixture of pieces of rock of various sizes and the remains of organisms. Fertile soil also contains air, water, some chemicals from the decay of living things, particularly plants, and various living things such as insects, worms and bacteria. The solid material beneath the soil is rock. There are many different kinds of rock with different compositions and properties. The action of wind and water wears down rock gradually into smaller pieces – sand is made of small pieces of rock and silt of still smaller pieces. About two-thirds of the surface of the Earth is covered by liquid water, which is essential to life. Water is constantly recycled through processes involving evaporation from oceans and other surfaces, such as soil and plants, condensation in clouds and precipitation as rain, snow or hail.
[241 words quoted.] (Harlen, W. (ed.), 2010, p. 32)

## For 11–14 years:

The layer of air at the Earth’s surface is transparent to most of the radiation coming from the Sun, which passes through. The radiation that is absorbed at its surface is the Earth’s external source of energy. Radioactive decay of material inside the Earth since it was formed is its internal source of energy. Radiation from the Sun provides the energy that enables plants containing chlorophyll to make glucose through the process of photosynthesis. The radiation from the Sun absorbed by the Earth warms the surface which then emits radiation of longer wavelength (infra-red) that does not pass through the atmosphere but is absorbed by it, keeping the Earth warm. This is called the greenhouse effect because it is similar to the way the inside of a greenhouse is heated by the Sun.
[133 words quoted.] (Harlen, W. (ed.), 2010, p. 32)

## For 14–17 years:

Oxygen in the atmosphere, produced by plants during photosynthesis, indirectly protects the Earth from the short wave (ultra-violet) part of the Sun’s radiation which is harmful to many organisms. The action of ultra-violet radiation on oxygen in the upper atmosphere produces ozone which absorbs this harmful radiation. The temperature at the Earth’s surface results from a delicate balance, which can be upset by adding gases to the atmosphere. Human activities produce carbon dioxide and methane which increase the greenhouse effect and leads to global warming and climate change.

Beneath the Earth’s solid crust is a hot layer called the mantle. The mantle is solid when under pressure but melts (and is called magma) when the pressure is reduced. In some places there are cracks (or thin regions) in the crust which can allow magma to come to the surface, for example in volcanic eruptions. The Earth’s crust consists of a number of solid plates which move relative to each other, carried along by movements of the mantle. Where plates collide, mountain ranges are formed and there is a fault line along the plate boundary where earthquakes are likely to occur and there may also be volcanic activity. The Earth’s surface changes slowly over time, with mountains being eroded by weather, and new ones produced when the crust is forced upwards.

[220 words quoted.] (Harlen, W. (ed.), 2010, p. 32)

These are examples from a part of the Science curriculum that everyone will be familiar with. It is set out here to illustrate how Big Ideas are developed into plans for a syllabus.

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