Ask your students to define length, height and width. Then explain the differences of each measurement to them. Ask students for examples of objects or structures that have length.
Give your students rulers or measuring tapes and let them loose on the classroom. Ask them to measure as many lengths as they can and record them on a sheet of paper. Reassemble the students and have them share what they have found. Make sure to have them justify why a measurement is a length and not a height or width.
Give students verbal problems to have them practice measuring length on a conceptual level. Create a scenario in which someone has to find out how long the side of his house is so he can paint it. Draw a picture of the wall and break it into even sections. Give the length of one small section and have students figure out the total length.