Children in early grades can learn to draw straight lines with rulers and to measure their length in centimeers and millimeters or inches and eights of an inch. To do so, they must learn how to align a ruler with the ends of the measured segments, and how to count "small spaces" between the lines on the ruler. They do not need to know fractions to be able to write and read the results of measurements. It is enough that they know that:
3 5/8 in means "3 inches and 5 out of 8 small spaces on the common scale".
But children need some tools to carry out operations of addition and subtraction on the
results of their measurements. (When this method of teaching metric measurements was
tested in the classroom, the children used four operation calculators, TI-108s,
made by Texas Instruments.)5.7 cm means "5 centimeters and 7 small spaces on the metric scale". Using Counting Boards With Variable Counters Arithmetic operations on measurements in inches can be done with variable counters that have the value 1/8. This means that one white token on the square labeled 1 can be exchanged for any configuration of variable tokens on locations whose values add up to 8. Similarly, computations done on metric measurements can be done with variable counters having the value 1/10. Common Scale
Let counter t have value 1/8. Let counter a have value -1/8. Common Scale Example 1: 2 3/8 in + 7/8 in
Common Scale Example 2: 5 6/8 in - 3/8 in
Metric Scale
Let counter d have value 1/10. Let counter b have value -1/10. Metric System Example 1: 4.3 cm + 1.6 cm
Metric System Example 2: 6.8 cm - .5 cm 6.8 - .5 = 6.3 Number Board index |