Draw a staircase with seven steps on a sheet of paper. Each step represents a different level of measurement and serves as a visual tool for fourth-graders when performing unit conversions.
Write the letter symbol above the step and the prefix underneath, starting with the top step. Label the top step "K" and write the prefix "Kilo-" underneath the top step. Continue with the rest of the steps: "H" represents Hecto, "D" for Deca, "W" for base unit, "d" for Deci, "c" for Centi and "m" for Milli. Notice that the letters after the "W" step are in lower case, which shows the units are smaller than the base unit.
Teach your fourth-graders about the three origin base units -- meters, liters and grams -- and how to convert them using the staircase diagram. For example, if you are trying to convert 5 milliliters (mL) into liters (L), begin with the "m" step and go up three steps to reach the "W" step, since liter is a base unit.
Add a decimal place after the number you are converting. For example, if the number is 5 mL, the decimal version would be 5.0 mL.
Move the decimal in the same direction you moved on the staircase diagram. For example, if you moved from milliliters to liters -- a total of three steps up and to the left -- you would move the decimal place three spots to the left. Therefore, a value of 5.0 mL would give you 0.005 L.
Repeat the conversion exercise with other values to ensure your students grasp the concept.