I taught a lesson this week that helped a teacher see why making direct comparisons and asking the right questions are so important to a young child's understanding of measurement. While this teacher thought her students had a good understanding of length because they were able to measure and compare using non-standard units of measure, she saw that they really did not understand what the word length meant, how having common baselines is important, and how one object was not necessarily longer than other just because you moved the position of it.
You can download the complete lesson plan, vocabulary, and key understandings here. I read a book, generated some discussion about length and making comparisons, modeled what I wanted them to do, then had them explore comparing length using play-doh.
I had students compare the length of play-doh snakes. They learned what length means, what a baseline is, and how to compare objects using longer than, shorter than, and the same as. It is important that we not only teach young children what these words mean but that we also have them put these meanings into their own words and use them when explaining their thinking.
I bought the Play-doh Mega Pack from Walmart for $19.99. It has 36 cans of different colored play-doh in it. I let students choose their own color, but asked that they choose a color different from their partner.