Maxwell-Week 13

Last week, my students started a new unit in math that focuses on measurement.  Although my students were able to understand the importance of using standard units when measuring, they held several misconceptions about measurement.  During one of our lessons this week, students were asked to measure a line segment in their student math workbooks.  The students were provided with 12 inch rulers. These rulers have both centimeters and inches written on them.  My MT announced to the class that the workbook is asking for a measurement of the line segments in inches, not centimeters, so it was important that they make sure their ruler was on the "right" side. 
Nearly all of my students were able to recognize the difference between centimeters and inches, and they quickly flipped their rulers around to begin measuring.  While watching one particular student, I noticed that he had measured several line segments starting with the "12 inch" end of the ruler.  I asked the student how he was measuring his lines.  He replied, "I am measuring in inches".  "Great job", I said.  Then, I asked why he was starting his measurements from the 12 inch end.  The student stated that since 12 was as big as the ruler got, it had to be a smaller size than that, so he was "measuring down".  His explanation made sense.  He could recognize that the line segment was smaller than 12 inches, therefore, the number of the measurement would be smaller than 12.  Measuring from zero made it seem like the line was getting bigger and thus had the possibilitity of getting a measurement above 12 inches, which my student knew was not a logical answer. I explained that we start from zero, because it will give us a clear answer to our measurement.  If the line ends at 5, then it is five inches long.  However, if we were to measure from the 12 side and the line stopped at 7, we wouldd have to perform a subtraction problem (12-7) to find our measurement in inches.