Year 4 science · Key Stage 2 · States of matter

Year 4 states of matter: solids, liquids, gases and the water cycle

In Year 4 science, children learn that materials come in three states: solid, liquid and gas. They compare and group materials by state, observe what happens when materials are heated or cooled, measure the temperatures at which changes happen in degrees Celsius, and use evaporation and condensation to explain how water moves around in the water cycle.

States of matter and the water cycle, explained

Children first learn to describe the three states in their own observable terms rather than with scientific models. A solid keeps its shape, even when it is moved from one container to another. A liquid flows and takes the shape of the bottom of its container; poured onto a table it forms a pool, not a pile. A gas, such as air or the water vapour in it, spreads out to fill any space it can and escapes from a container that is not sealed. Some materials are tricky. Sand pours, but each grain is a tiny solid. Foam and toothpaste do not fit neatly into one group, which is a good chance to discuss why groups sometimes need careful rules.

Next, children observe that heating or cooling can change a material’s state. Water is the main example, because it can be seen as ice, liquid and water vapour. Melting turns a solid into a liquid and freezing turns it back; evaporation turns a liquid into a gas and condensation turns a gas back into a liquid. Children measure temperatures with a thermometer in degrees Celsius, noting that water freezes and ice melts at 0 °C and that water boils at 100 °C. Many schools also research other materials, for example that iron melts at around 1,538 °C. To keep to physical changes that can be reversed, teachers avoid examples where heating changes the material permanently, such as baking a cake or burning wood.

The water cycle puts these changes together. The sun warms water in seas, lakes and puddles, and some of it evaporates into the air as water vapour, which is invisible. Higher up, the air is cooler, and water vapour condenses into tiny droplets of liquid water that form clouds. When the droplets join and become heavy enough, they fall as rain, hail or snow, which is called precipitation. The water runs into rivers and the sea, or soaks into the ground, and the cycle starts again. Evaporation happens at any temperature, not only when water is boiling, but it happens faster when things are warmer, which is why washing dries faster on a warm, breezy day than on a cold, still one.

Observation matters as much as explanation. Schools may ask children to watch a puddle shrink on a dry day, to see how quickly different liquids evaporate, or to explore how temperature affects chocolate, butter or cream. They are not expected to explain these changes in terms of particles at this age, which comes later.

Words your child will hear

Solid, liquid, gas: The three states of matter. Solids keep their shape, liquids flow and take the shape of their container, and gases spread out to fill the space.
Melting and freezing: Melting is a solid turning into a liquid. Freezing is a liquid turning into a solid.
Evaporation: A liquid turning into a gas. Water evaporating becomes water vapour in the air.
Condensation: A gas turning back into a liquid when it cools, such as droplets on a cold window.
Water vapour: Water in the form of a gas. It is invisible.
Degrees Celsius (°C): The unit used to measure temperature in science. Water freezes at 0 °C and boils at 100 °C.
Water cycle: The way water moves between the sea, the air and the land through evaporation, condensation and precipitation (rain, hail or snow).

What the National Curriculum says

In Year 4, pupils should be taught to:

Compare and group materials together, according to whether they are solids, liquids or gases
Observe that some materials change state when they are heated or cooled, and measure or research the temperature at which this happens in degrees Celsius (°C)
Identify the part played by evaporation and condensation in the water cycle and associate the rate of evaporation with temperature

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

Try it: explaining how washing dries

Two identical wet flannels are hung up, one in a warm room at about 22 °C and one in a cold garage at about 8 °C. After two hours, which is drier, and why?

Identify the states. The water in the flannels is a liquid. As the flannels dry, some of that liquid is changing into a gas, water vapour, which spreads into the air and cannot be seen.
Name the change. A liquid turning into a gas is evaporation. It does not need the water to be boiling: it happens at the surface of the water at room temperature and below.
Predict using temperature. Evaporation is faster when things are warmer, so the flannel in the warm room should lose its water faster and be drier.
Check the test is fair. The flannels must be the same type and size, wrung out in the same way, and hung up for the same time. Only the temperature should be different.
Link to the water cycle. The same thing happens to puddles, ponds and the sea. If the vapour reaches colder air or a cold surface, it condenses back into tiny drops of liquid, which is how clouds form and why a cold window mists up.

The flannel in the warm room is drier because evaporation (liquid water turning into water vapour) happens faster at a higher temperature. The water has not disappeared: it has become water vapour in the air.

Common mistakes and how to help

Thinking evaporation only happens when water boils

Children see steam from a kettle and link “turning into a gas” with very hot water. They may not connect it with a puddle disappearing on a cool day.

What helps: Put two equal saucers of water in different places, such as a sunny windowsill and a cool shelf, and compare them over a few days. Evaporation is slow when cool, but it still happens.

Believing the cloud of steam from a kettle, or the clouds in the sky, is water vapour

Water vapour is a gas and invisible. The white cloud that you can see is made of tiny drops of liquid water that have already condensed.

What helps: With an adult handling the kettle and everyone standing well back, look at the gap between the spout and the start of the white cloud. Children can often see a clear space there. That clear space is where the water vapour is.

Believing water on the outside of a cold glass has leaked through from the inside

It looks as though the drink is seeping through, because the drops form where the glass is cold. It is natural to look for a path from one to the other.

What helps: Try a glass of ice water and a glass of water at room temperature. Only the cold glass collects drops. The drops come from water vapour in the air condensing on the cold surface.

Thinking air is “nothing”, or that gases are not matter

Air cannot be seen and does not feel heavy, so children conclude it is empty space.

What helps: Show that air takes up space: blow up a balloon, or push an upside-down cup into a bowl of water and notice that the cup stays mostly dry inside.

How to help at home

Ice cube observation. Place an ice cube in a bowl at room temperature and another somewhere cold, such as a fridge shelf. Watch them over time and predict which will melt first. Use a thermometer on a shelf or in the room to record the temperatures.
Washing line science. When hanging out clothes, ask whether they will dry faster indoors or out, in sun or shade, on a windy day or a still one. Next time, check your prediction.
Puddle watch. Mark round a puddle in the garden or a quiet park with chalk after rain and check it at intervals during a dry spell. Ask where the water has gone and what it might be doing now.
Mist a mirror. Breathe on a cold mirror or the outside of a cold window and watch it mist up and then clear. Talk about which way the water is changing state each time.

Everything in Year 4 science

Updated 20 October 2026.