Years 3 and 4 science · Key Stage 2 · Working scientifically

Years 3 and 4 science enquiries: fair tests and measuring

Working scientifically is the part of the primary science curriculum about how scientists find things out. In Years 3 and 4, children ask their own questions, decide what kind of enquiry will answer them, set up simple fair tests, make careful observations, measure in standard units and record what they find. It is always taught through the other topics, such as plants, rocks or forces, rather than as a separate unit.

Fair tests and enquiries, explained

Not every scientific question is answered by a fair test. In Years 3 and 4, children learn that there are several kinds of enquiry and begin to choose the best one for their question. They might observe something over time (how a bean grows), look for patterns (do taller people have bigger feet?), group and classify (sorting leaves or rocks), carry out a comparative or fair test (which paper towel soaks up the most?), or use books and other sources when an experiment is not possible, such as finding out how fossils form. Teachers help pupils to see that “Which is the best?” might need a test, while “What lives in the garden?” needs careful looking.

A fair test means changing one thing, measuring one thing and keeping everything else the same. The thing that is changed is sometimes called the independent variable, but at this age you will more often hear “what we change”, “what we measure” and “what we keep the same”. With help, children decide how to set up a test, such as using the same amount of water for every plant but a different amount of light. Some classes also begin to repeat a test to check a result, which becomes more important in Years 5 and 6.

Careful observation and accurate measurement are the second big focus. Children are expected to use standard units: centimetres and metres for length, grams and kilograms for mass, millilitres and litres for capacity, degrees Celsius for temperature and seconds for time. They use rulers, measuring jugs, scales and thermometers, and they learn to read these accurately. The curriculum names thermometers and data loggers in particular. A data logger is a small device with a sensor that records something such as temperature, light or sound automatically over time, so it can track changes a person would find hard to follow by eye, such as how quickly a cup of warm water cools.

Finally, children learn to collect and present data: first in notes and simple tables, later in diagrams and charts. They also use simple keys, which are a set of yes or no questions that lead to the name of a living thing or object, to sort and identify. They are not expected to do all of this independently at once. Much of it is done with help: teachers share the thinking and model each step, and children gradually take on more of the decisions themselves across the two years.

Words your child will hear

Enquiry: A way of finding something out, such as observing, grouping, testing or researching.
Fair test: A test where only one thing is changed and everything else is kept the same.
Variable: Something that can change in a test, such as the amount of water or the type of surface.
Prediction: What you think will happen and why, before you test it.
Standard unit: An agreed measurement such as a centimetre, gram or degree Celsius, so results can be compared.
Data logger: A device with a sensor that records measurements, such as temperature, automatically.
Key: A set of questions with yes or no answers used to sort or identify things.

What the National Curriculum says

In Years 3 and 4, pupils should be taught to:

Ask relevant questions and use different types of scientific enquiries to answer them
Set up simple practical enquiries, comparative and fair tests
Make systematic and careful observations and, where appropriate, take accurate measurements using standard units, using a range of equipment, including thermometers and data loggers
Gather, record, classify and present data in a variety of ways to help in answering questions

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

Try it: planning a fair test

Which of three kinds of kitchen paper soaks up the most water?

Turn the question into something that can be tested and make a prediction. “I think the thickest paper will soak up the most water because it has the most paper to hold the water.”
Decide what to change: the type of kitchen paper. There are three different types, so there are three tests.
Decide what to measure: how much water is soaked up. One way is to pour 100 ml of water into a bowl, dip a sheet in for 10 seconds, lift it out and let it drip back into the bowl for 5 seconds, then pour the water left in the bowl into a measuring jug and read it. The less water left, the more the paper soaked up.
Decide what to keep the same, so the test is fair: the size of the sheet, the starting amount of water, the dipping time, the dripping time and the measuring jug.
Record the results in a table with a row for each paper and units in the heading (ml). Do each paper three times so that one odd result can be spotted, and compare the three for each paper.

The plan changes only the type of paper, measures the water left in the bowl in millilitres, and keeps the sheet size, water amount and timings the same. Each paper is tested three times and the results are put in a table. The paper that leaves the least water in the bowl is the most absorbent.

Common mistakes and how to help

Thinking every science question needs a fair test

Fair tests are the most memorable kind of practical work, so children assume they are what science is.

What helps: Sort some questions together. “Which ball bounces highest?” can be tested; “How do snails move?” needs observing; “How do volcanoes form?” needs research. Ask your child which type fits.

Changing more than one thing at once

Children are keen to make things better. They may use a different plant, a different amount of water and a different pot, then cannot say which change made the difference.

What helps: Say it as a rule of three: change one thing, measure one thing, keep the rest the same. Ask “What are we keeping the same?” before every test.

Measuring by eye instead of with units

Words such as “quite far” or “a bit more” feel quicker, and children don’t always see that others cannot compare them.

What helps: Ask “How could we tell someone else exactly how far?” Let your child choose the right tool and give a number with a unit, such as 35 cm or 120 ml.

Believing an unexpected result means the test has failed

Children think of science as getting the right answer. A result that does not match their prediction can feel like a mistake.

What helps: Treat surprising results as interesting. Ask what might explain it, whether the test was fair, and whether repeating it gives the same answer. A prediction that is wrong is still good science.

How to help at home

Ask “How could we find out?”. When your child wonders something, such as which towel dries fastest or which toy car rolls furthest, ask what they would change, what they would measure and what they would keep the same. You don’t have to run the test every time; planning it is good practice.
Measure in real units. Let your child use a ruler, kitchen scales, a measuring jug and a room thermometer while you cook or tidy. Give a number and a unit each time, and compare with an estimate made beforehand.
Make a simple key. Choose six things, such as toys, shoes or leaves. Together write yes or no questions (“Does it have laces?”) that split them into smaller groups until each item has its own place.
Run a repeat test. Roll a toy car down a tray propped on books and measure how far it goes three times. Talk about whether the three distances match, and what could have made them different.

Builds on

Key Stage 1: Working scientifically

Leads on to

Years 5 and 6: Working scientifically