When pregnant women arrive at the maternity ward, one of the first questions they are asked is the size of their feet. The information so gathered is an everyday use of the scientific enquiry skill of association. But how?

Association is one of the practical skills of the new national curriculum scientific enquiry target. Association is looser than cause and effect. It is one way of looking at complex relationships, like those between human beings and their environment.

The topic “ourselves” is full of associations - for instance, between smoking and lung cancer, or between over-eating and obesity. But for every connection of this kind, there are exceptions - the long-lived smoker, the thin person who eats like a horse. People are too complex to make firm links in every case. But you can recognise a tendency, a pattern or trend.

There is a pattern linking shoe size to ease of childbirth. Large feet can indicate large bones, large bones can indicate wide hips, and wide hips can mean it will be an easy birth. But this is an association - not a link. Small feet do not guarantee a difficult birth, and large feet do not guarantee an easy one.

The understanding of association begins in infant school: “I’m older than you, so why aren’t I taller?” We encourage exploring associations by making simple body comparisons. Have the tallest people got the largest hands? Drawing round ourselves and pinning our outlines to the wall in height order shows our relative sizes.

Overlaying children’s ages, or foot or hand outlines, shows that these are not in step with their height; and, of course, relative dimensions will change as the children get older.

There are further familiar “rules of thumb”. It is suggested that if you double a child’s height when they’re four you can predict their height when fully grown. Also, the distance from fingertip to fingertip, with your arms outstretched, is supposed to be the same as your height.

Humans are often said to fall into three general body shapes - “endomorphs” tend to be spherical and “ectomorphs” to be slender, while “mesomorphs” have a “cubic” head and heavy build. Experience suggests that we are all endomorphs in our bathroom mirror.

It is important to handle any body measurements and comparisons with sensitivity. My own son grew slowly and late, and was always at the bottom of any bar chart. His teacher, sensitive to his disappointment, created an activity where the children had to curl up inside ever smaller hoops. Only James - to everyone’s envy - could fit inside the smallest.

For older children, association can be a powerful tool for exploring “ourselves” through information technology. It is a good opportunity for collecting data and making graphs.

This is one way of exploring associations between body sizes and physical abilities. There are potential sporting connections. The Australian Olympic swimmer Ian Thorpe (called “the Thorpedo”), with his size-16 feet, had effectively got flippers on. But are big feet essential to Olympic swimming success? There might be other sporting examples - boxers with big hands, perhaps?

The tallest people might be expected to jump the highest (not true, as it turned out - my class argued that smaller people were lighter, and so could jump higher).

But people also defy expectations: surgeons and musicians often have short, stubby fingers.

The prediction of adult height is a superstition, as is the assertion that “boys always grow to be taller than their mothers”. Heredity is more complex than that. But there is a lot of mileage in investigating the truth in such old wives’ tales. You could check your sock size by wrapping a sock round your fist. If the association is correct, the sock that fits your foot should encircle your fist exactly.

The ancient Egyptian method of measuring was based entirely on the relationships between body parts. The thickness of four fingers - four “digits” was thought to be equal to a palm; and seven palms to a cubit - the distance from elbow to the tip of the middle finger.

The English inch was originally defined as the width of a thumb; the yard was the distance from a man’s nose to the tip of his outstretched arm; and the foot was just that - toe to heel. Are these definitions accurate? And for whom?

Try exploring some associations. It will help children to understand why even the most educated adults struggle to make links between different factors - between BSE and CJD; or between the MMR vaccine and autism, for example.

A new study has just shown that school performance is related to birth weight. The heavier they were at birth, the better that child will do at school. Should you be asking for a child’s birth weight before admitting them to your school? I don’t think so. People are not as simple as all that.

ARE THESE TRUE?

* The tallest people in the class have the biggest feet.

* The shortest people in the class have the smallest hands.

* The people with the longest legs can make the longest or highest jump.

* The people with the widest hand-span can hold the most marbles in a closed fist.

* The distance from wrist to elbow is the same as the distance round your head.

* The measurement round your closed fist is the same as the length of your foot.

* People with the smallest neck measurements have the thinnest wrists.

WARNING: Don’t allow children to take body measurements, such as lung capacity, that could lead to competitiveness and risk.