Most standard rulers have many different units of measurement: centimeters, feet, inches and fractioned inches. Explaining thoroughly what each unit of measurement represents, using body parts as symbols, will help students to better express measurements. Play a multiple choice game asking students to choose the correct unit of measurement for common classroom objects. Practice with non-standard rulers, as well, such as yard sticks and tape measures.
Once students grasp different units of measurement, they're ready to use a ruler. Make sure that the student not only is using the numbered side of the ruler, but also that the object is lined up with zero and not necessarily the edge of the ruler. Measuring actually takes a lot of coordination for children because they must use both hands to line up an object and move their eyes from one side to the other. Help them by holding the object steady.
Many objects do not measure exactly to the inch mark, and since they fall between two numbers, children often get confused as to which number to read. They may read an object that is 4 ½ inches as 5 ½ inches. Practice following the numbers on the ruler with a finger until the last whole number before the end of the object. Have the children say the number aloud or write it down before moving on to the fraction.
Units smaller than an inch pose the biggest problem to students learning to use a ruler. Before they can accurately read a measurement, they must understand fractions, that an inch is divided into eights and that each mark on the ruler represents 1/8. (A metric ruler is divided into tenths.) Teach them that 4/8 is the same as 1/2 (reads "one half"). They must learn to count the ruler marks and then think about the fraction before saying or writing it. Rather than having them always measure an object or line, have your students draw a line of a certain measurement for practice.