Science · Year 4

Solids, liquids and gases: Year 4 science

By Dave Allen · Updated 5 October 2026 · 5 min read

Drafted and fact-checked with AI help, against the sources below. Not yet reviewed by a teacher. How we write our guides

What it is

States of matter: Matter is anything that takes up space. It comes in three main states: solid, liquid and gas.
Change of state: When a material turns from one state into another, such as ice melting into water. Many of these changes can be reversed.
Evaporation: When a liquid turns into a gas. Water evaporates from a puddle after rain, without needing to boil.
Condensation: When a gas cools and turns back into a liquid, like the water droplets on a cold bathroom mirror.

Each state behaves in its own way. The curriculum's guidance gives children three simple tests to tell them apart:

Solids hold their shape. A stone, a spoon or an ice cube stays the same shape wherever you put it.
Liquids form a pool, not a pile. Water, milk and honey flow and take the shape of their container, but the amount stays the same.
Gases escape from an unsealed container. A gas spreads out to fill any space it's in, and most gases are invisible. The air inside a balloon is a mixture of gases.

Water is the star of this topic, because children meet it every day as a solid (ice), a liquid (water) and a gas (water vapour or steam).

How it's taught at school

States of matter is a Year 4 topic in the national curriculum for England. Children are taught to:

compare and group materials 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 where this happens, in degrees Celsius (°C)
explain the part evaporation and condensation play in the water cycle, and link faster evaporation with higher temperatures

Children learn the names of the changes: melting (solid to liquid), freezing (liquid to solid), evaporating (liquid to gas) and condensing (gas to liquid). The temperature where a solid melts is its melting point, and the temperature where a liquid boils is its boiling point.

Ice melts:      0 °C
Water freezes:  0 °C
Water boils:  100 °C

The key temperatures for water

In the water cycle, the sun warms water in seas, rivers and lakes and it evaporates. The water vapour rises, cools and condenses into droplets that form clouds. When the droplets get heavy, they fall as rain, snow or hail, and the water makes its way back to the sea.

Lessons are very hands-on: melting ice or chocolate, watching a puddle shrink, or seeing how fast washing dries on a warm day. The curriculum asks teachers to avoid heating things that change for good, such as baking or burning, because those aren't changes of state.

Tip
Your kitchen is a science lab for this topic. The freezer, a glass of water and a cold window cover almost everything your child needs to see.

From Pipkin

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Common mistakes (and how to help)

Calling sand, sugar or flour a liquid because it can be poured: Use the pool-or-pile test. Pour some sugar on a plate and it makes a pile; pour water and it makes a pool. Each tiny grain is a solid that holds its own shape.
Thinking gases aren't really anything: Gases are matter too: they take up space even though we usually can't see them. Blow up a balloon together, or squeeze an empty plastic bottle with the lid on and feel the air push back.
Thinking water only evaporates when it boils: Water evaporates slowly at everyday temperatures too, which is why puddles dry up and washing dries on the line. Heat just makes it happen faster.
Mixing up melting and dissolving: When ice melts, one material changes state on its own. When sugar disappears into tea, it's mixing with a liquid, which is called dissolving. Children learn about dissolving in Year 5, so for now it's enough to know they're different.

Three quick activities at home

Ice cube race

About 5 minutes · You need: Ice cubes and a few saucers

Put one ice cube on each saucer and place them around the house: by a sunny window, in a cool room, near a radiator.
Ask your child to guess which will melt first, and why.
Check back every so often. Talk about how heat makes a solid melt into a liquid.

Pool or pile?

About 5 minutes · You need: A tray or plate, water, and something like rice or sugar

Pour a little rice onto one side of the tray and a little water onto the other.
Ask your child which one made a pile and which made a pool.
Hunt around the kitchen for more materials and sort them into solids, liquids and gases. Is the air in a crisp packet a gas?

Window drops

About 5 minutes

After a bath or shower, or while a pan is steaming, look at a cold window or mirror together. A grown-up stays in charge of anything hot.
Ask where the water droplets came from. Water vapour in the air cooled on the cold glass and condensed back into a liquid.
Leave the room and come back later. Have the droplets gone? That's evaporation, taking them back into the air.

Try it with your child

Free Pipkin puzzles on this topic. No sign-up. They open on the children's side of Pipkin.

Questions parents ask

Does my child need to learn exact temperatures?

The curriculum asks children to measure or research the temperatures where materials change state, in degrees Celsius. For water, 0 °C for freezing and melting and 100 °C for boiling are the key ones to know.

Why do water pipes sometimes burst in winter?

Water takes up more space when it freezes, by about 9%. If the water in a pipe freezes, it can push hard enough to crack the pipe. It's a real-life example of a change of state.