As I was planning for a summer PD, “Decimal Fluency Built on Conceptual Understanding”, I was going through pictures of my students’ work. I focused on the very first multiplication problem I had presented to them in which both numbers were less than a whole. I presented them with 0.2 x 0.4 and asked them to do a “Notice/Wonder” and think about the product. I had anticipated some may reason using fraction equivalents, some may know that .4 is close to half and take half of .2, and some may try fraction bars or arrays to solve. Here are samples of their initial work….

As I circulated the room, the two products that showed up were 0.8 and 0.08, as I anticipated. I put them on the board and had the students work through it as a group and try to prove the product they thought was correct and disprove the one they thought was incorrect (I did not tell them at this point, that was their job!:)

During the share out, this is the one response I did not anticipate at all and now, going back, I wish I had spent more time with…grrr….darn hindsight!

For all of the nerdy math peeps, like me, who like to “figure things out” I am going to leave out her explanation here! I will gladly recap it for anyone who would like to hear it in the comments or via twitter!

Needless to say it left many students a little baffled, and we did revisit it the next day for her to re-explain her reasoning. I just wish I had extended this by asking students if this model would work for any two decimals less than one whole? Why does it work with .2 of .4?

I highly recommend snapping pictures of your students’ work all year long because reflecting back on this work over the summer has taught me a lot about anticipating student responses and how to handle those responses you just don’t expect! It also just makes me smile at the way my students reasoned about the math we were doing!

-Kristin

Here are a few pictures of the follow up group work and Gallery Walk they did with 0.5 x 0.3….