Teach children the metric base units for length and distance, weight and volume. Explain that length and distance are measured in meters, weight in grams and volume in liters. Ask what units would be appropriate for different measurement tasks, such as determining the length of a wall, measuring the amount of milk in the carton or discovering how much a book weighs.
Explain that the base unit indicates what aspect is being measured and the prefix tells the size of the units being used. Metric prefixes are based on the decimal system. Have the students memorize the prefixes in order from large to small with the mnemonic "Kings have diamonds, but diamonds cost money." The first letter of each word matches the prefixes in descending order: Kilo-, hecto-, deka-, base unit, deci-, centi- and milli-. Repeat the appropriate measure activity, this time using an appropriate prefix as well as correct base unit. Ask questions, such as whether bathwater should be measured in liters or milliliters? Ask students if the distance between cities would be calculated in centimeters or kilometers.
Make a graphic display of the prefixes in order from largest on the left to smallest on the right. Put the base unit in the center. Create a movable decimal point. Demonstrate to students how to write any measurement number using each of the units. Choose a number and position it on the graph such that the one-place digit is in the column of the prefix being used. Add the decimal point to the right of that number. For example, for 72 grams, write the numeral 2 in the base- unit column and put the decimal on the line to the right of the two. To calculate the number of milligrams in 72 grams, just move the decimal point to the line after the milligrams column. Add zeros in the empty columns and read the new number. It will be 72,000 milligrams. To discover the number of kilograms in 72 grams, just reverse the process. Move the decimal point to the line on the right of the kilograms column. Add zeros between the 72 and the decimal point, so 72 grams is equal to .0072 kilograms.
Connect the concept of powers of 10 to the process of changing metric units into larger or smaller pieces. Each prefix moving to the left is larger by a factor of 10 than the one before it. Each prefix moving to the right is smaller by a factor of 10. Use graphic aids to help students understand the calculation until they are able to make similar calculations mentally. Use a calculator to check the accuracy.