I was in a 2nd grade room the other day and a teacher was presenting a lesson on measurement using customary units.  Students were using rulers to measure to the nearest inch.  One of the students asked, “what if it is over 4 inches but not 5 inches?”  The teacher said, “you choose.”   I walked over and whispered, “actually let’s round up if it’s at a half and down if it’s before half because when they use rounding in 3rd grade next year, that will provide them the visual representation to refer back to.”

This really got me thinking again about the power of vertical teaming.  This teacher didn’t know that this is a common misconception in 3rd and 4th grade.  She also didn’t know many of the misconceptions around measurement.  She anticipated that they might start with something other than zero, but she didn’t know to address that in 2nd grade we are measuring units without precision and that vocabulary such as “about 5 inches” is necessary.  Or that conversations about which one to choose would be necessary.  In the task below for standard 2.MD.A.2, I hope to have students dig into discussions about which number to choose and why.  I want them to defend their reasoning and discuss which would be more accurate.  This will allow students to reason with numbers and will carry over to rounding, to estimation, and to looking for reasonableness in their answers in years to come.

The Common Core Standards specifically state in 1.MD.A.2 to ” Limit to contexts where the object being measured is spanned by a whole number of length units with no gaps or overlaps.”  That is the reason that I used standard 2.MD.A.2 for this task.  In my opinion, this task is very appropriate for first grade and kindergarten students as well.  That conversation cannot happen early enough!

Act 1:

About how many ducks long is the math rack?

About how many cubes long is the math rack?

Act 2:

About how many ducks long is it?  Why did you choose that number?

There are 4 more cubes than ducks.

About how many cubes long is it?

Act 3:

Were you correct?

If so, what were you thinking?

If not, what was your thinking?