The activities in this section are concerned with the measurement of
length and angle.
Practical measuring activities relating to length, weight, capacity etc.
have long been a common feature of the mathematics work in Infant classrooms
and are usually well represented in the published materials available
to schools. Unfortunately, soon after this, in the Junior years, it is
all too often assumed that most children know what measurement is and
have clearly grasped the need for standard units of measure. As a result,
much of the work presented to children in this age group tends to consist
of manipulation of standard units (more 'sums' in disguise) and practice
in the use of ready-made measuring instruments. Experience indicates that,
in many cases, such assumptions are unfounded. The essential ideas involved
in measurement (the comparison and quantification of continuous quantities)
are subtle and will be learned by children not from teacher explanation;
but by experiencing them over a protracted period of time in many different
contexts.
The ideas in measurement are:
Measurement is essentially an approximate affair. All measurements
are inherently inexact. 'Progress' in coming to terms with measurement
therefore typically takes the form of a sequence of activities beginning
with crude global comparisons ('bigger than', 'lighter than' etc.),
leading to the use of arbitrary units.
No particular magic resides in the use of standard units such as the
centimetre, kilogram or litre. These are adult conventions and all the
basic work on measurement done with young children could readily be
done with informal units that are meaningful to them - the ideas involved
are exactly the same. Indeed, the continued use of informal units beyond
the Infant years may help many children to eventually realise this.
(At some stage the 'turtle unit' could be redefined to emphasise the
arbitrary nature of such units).
The approximate nature of such measurement implies that any measurement
involves an 'error' - not a mistake but simply a discrepancy between
what was expected and what was obtained, or between an estimate and
an actual measurement. Such 'errors', or deviations, will normally become
smaller and smaller, the degree of accuracy obtained being eventually
expressed using decimal numbers.
Throughout all measuring activities, estimation of quantities before
measurement is of vital importance. Estimation is an essential component
of every activity and the natural unit of length in this context is
the 'turtle unit'. In the case of the Valiant Turtle this is very close
to a centimetre so that the link with standard units can be readily
made when needed.