At the very start of teaching a unit on measurement, the first thing to do is introduce students to the tools we use to measure. Ask the students to brainstorm what tools they can think of that are used for measurement. They might name rulers and tape measures, measuring cups and spoons and protractors and scales. They might also include things such as thermometers and scales or non-standard measuring tools such as feet or hands. See how many tools they can name and talk about how they are used.
Demonstrate to students the proper way to use a ruler or tape measure to measure the length of an object. Select a list of objects in the classroom for the students to measure and then ask the students to measure them. When they are finished, write the name of the first object you gave them on the board and ask for their results. More than likely, there will be different numbers. Talk about why this happened and how careful you need to be when measuring things to make sure you are accurate.
Introduce the students to tangrams, which are Chinese puzzles that are squares cut into seven geometric shapes that can be arranged into different shapes. Have the students figure out the area of the puzzle when it is in a square. Then have them use the tangrams to make new shapes. When they are done, ask them to find the area of the new shape they have made. Then talk about their findings.
Divide the class into groups. Provide each student with a 1-gallon container, as well as containers measuring a quart, a pint, a cup and an ounce. Tell the students to figure out how many quarts, pints, cups and ounces a gallon will hold, using the containers and water, but do not give them any more guidance than that. Ask them to write down their findings on a piece of paper. Then talk about their results and methods when they are finished.