The activity that sold me on this resource came from the measurement chapter of this resource. It suggested giving the students a broken or unnumbered ruler and having them measure an object to truly gauge whether they understand how to use a ruler or not. Let me tell you... I was BLOWN AWAY. I took an old wooden ruler and broke the zero end off. When I handed it to each of my students in a one-on-one conference, easily half of them couldn't do it! The looks on their faces were priceless, really. Many of them lined the object up where they thought the zero might have been. Others lined it up with the first full line and measured from there, not taking into account that the number wasn't zero. Still others simply told me it wasn't possible to measure the object since the zero was gone. Those who came closest lined the object up to the ruler and then proceeded to count the lines, ending up with a measurement that was one unit too high.
What this activity taught me was that students learning about using a ruler needed to understand that it was the spaces, not the lines, on the ruler that they were really counting when measuring something. By the time they got to me in fifth grade it was often too late - they had those habits already. Well... now I've got them early! :)
Today in my grade 2/3 classroom we explored unnumbered rulers. First we highlighted the parts of the ruler on a worksheet: the first line (where we typically begin measuring from), the measuring edge (vs the opposite side of the ruler), and then we added smiley faces in the spaces between the lines - to really focus our attention on the spaces - and after this they did some measuring for me. Every single one of them got it!