I got my copy of Teaching Children Mathematics over the weekend, and I read an article about measurement misconceptions. One of the big misconceptions when kiddos measure with a ruler is what is calledtick counting. What that means is that instead of counting theunits between the ticks on the ruler, kids count the tick marks instead. It's important that kids have LOTS of practice measuring with nonstandard units to prevent the tick counting error. When they measure using, for example, paper clips, there are no tick marks, so they realize the unit is the length of the paper clip. A line segment is 5 paper clips long. Inch color tiles are a good transition from nonstandard units to a ruler because kids can use both the color tiles and a ruler to measure the length of objects. The measurements should match!