Examples of what pupils should know and be able to do
Recognise when an exact answer is not needed and an estimate is sufficient, or when an exact answer is necessary and an estimate is insufficient.
Know that:
Sometimes there are different ways for finding an approximate answer.
More than one approximation to the same calculation is possible.
Explain how to estimate an answer before using a calculator to work it out.
Probing questions
What are the advantages of estimating answers before calculating?
Talk me through your thinking when deciding how to get a reasonable estimate for a calculation, for example:
103 × 0.44
√(16.1)
What if pupils find this a barrier?
Give pupils plenty of opportunities to practise using and justifying estimates. Encourage pupils to use the context of a problem to check whether an answer is sensible. Highlight the different ways of rounding by encouraging pupils to use their own strategies and then discussing or evaluating them.