Estimating length: Begin by measuring small everyday objects found around the house. Take a remote control, a book, and a crayon. Compare the three. Ask the student which is bigger. Take the longest object (most likely the book) and compare its length against a T.V. set. Which is bigger? Most likely the T.V.. Now without directly comparing the remote to the television ask the student which they think is longer. They can draw upon the previous comparison to the book.
Try this again with other objects. You can try the alternative where you take the smallest object and compare it to something even smaller. Then ask if the smallest object would be bigger or smaller than the other objects.