Parents who thought children were taught only in metric measurements these days might be surprised to find yards, feet and inches in England's brand new national numeracy strategy.

They are part of the "mathematical vocabulary" that children are expected to be comfortable with by the time they leave primary school - which could be useful if they are planning to become Nasa engineers.

Also in there are pints and gallons, and pounds and ounces. And there are a few other things that might come as a surprise.

Parents keen to help with their children's homework - as the government is encouraging them to - are anxious about 'getting it wrong' and conflicting with what schools are doing.

It can be all too easy, because things have probably changed since they themselves were at school.

Confronted with the subtraction sum 62 minus 28, mum or dad might naturally put the biggest number above the smaller, draw a line underneath, and set about 'borrowing' from the tens column.

No more borrowing

But not only is there more than one way of doing that, they should know that their children probably will not encounter that sort of 'column subtraction' until their fourth year of school.

Even then, 'borrowing' is not a word the children will recognise: it has been replaced with 'exchanging'.

Younger pupils are more likely to use a 'number line' to work out the answer.

Number lines are graphical ways of showing the relationships between numbers and arithmetical steps between them, and help children to visualise what they are doing.

Take the sum 84 minus 56. One way of establishing the difference between the two numbers, which is what subtraction means, is to work upwards in more manageable steps, until you arrive at the desired figure: from 56, add 4, then 20, then another 4, which equals 28.

The number line version is:

Alternatively you can take the 56 from the 84 by 'taking too much and giving some back', again to break it into more manageable chunks. So take away 60 (too much) and add back the difference between 60 and the number it should have been, 56:

Once column subtraction does arrive, the children are likely to work to a 'decomposition' strategy - breaking bigger numbers down into smaller components.

In these examples (right), the third method of exchanging tens for units, to make the subtraction manageable, is likely to be preferred as being the clearest way of writing down what is happening.

They will already know about 'partitioning'. That sounds like a big word for small children, but in these numeracy strategy days it means simply the separating of numbers into units, tens, hundreds, and so on.

This is used also in multiplication. For example, 346 x 9 is nine times three hundreds, four tens and six units: three separate sums that can be done easily, with a grasp of the times tables, then added up.

So 9 x 300 = 2700 plus 9 x 40 = 360 plus 9 x 6 = 54, makes 3114.

As a check, children are taught always to approximate first, so will have started with "346 x 9 is roughly 350 x 10, which is 3500" - giving them a ballpark figure for the answer.

Tight schedule

One of the things that has most struck teachers about the numeracy strategy, even more than the literacy strategy - and has prompted complaints about its being "too prescriptive" - is that it follows a very brisk timetable.

This is not quite on the level of 'if it's the third Friday of term we'll be doing fraction notation' - but it is not far off it.

The lesson plans set out in the Department for Education's hefty ring binder, Framework for teaching mathematics from Reception to Year 6, include grids for teachers to tick off where they have got to.

Certain subjects are given a prescribed amount of time, then the class must move on to another topic. If they do not, they will never get through the whole scheme.

One effect of this is that if a child misses even one day, for whatever reason, it is harder than ever for them to catch up.