Someone took the 11 card! A Teachable Place Value Moment

Something amazing happened today.  I was about to start a whole group lesson in first grade when a student shouted out "someone took the 11 card."  Now a student in first grade shouting something out when they are not supposed to is not the amazing part.  The amazing part is that we are a few days into a unit on geometry and I was planning to use my whole group instruction time to look at attributes of shapes and do some 2-dimensional shape sorting.  Quite often with first graders I will have a first grader who speaks when it is not their turn and usually I go on with things, but this time was very different.



This students' interruption caused me to change my plans for the first ten minutes of class.  Completely changed.

Here is what the student was talking about

These are arrow cards.  I use them to help kids learn to read and write numbers (and much more!) If you have not seen these used in the classroom, check out my guest post at Kid's Math Teacher.  

Anyways, I noticed last week when I did some formative assessment that 5 students in this first grade classroom were having a hard time seeing the teen numbers as ten and some more.  The student who shouted out that the 11 card was missing was one of these kids.  

I decided right then and there to seize the opportunity and see where it would go.  I am so glad I did!

I jumped right on the comment and asked her how she knew the 11 card was missing.  She replied "because I don't see it."

Not exactly what I meant so I tried again.  "Where does the 11 card belong up here?"

After a 10 second pause she says "It goes right after the 10."

By now most of the rest of the class has their hands up and are wiggling in their seats.  She can tell that they know something she doesn't.

I ask other students if they have seen me show the number 11 on the arrow cards and they all agree that I have.  I then ask students to give a hint about what might have happened to the 11 card.  

A very nice young lad tells her so kindly, "you need to use 2 of the other cards to make the 11 card."

She thought about that for a bit and then I could see the light-bulb moment of her getting it.  With great enthusiasm, she rushes up to the board, grabs the 10 and 1 cards, put the arrows on top of each other and proudly exclaims that she found the 11.  I then wanted to push it a bit farther for her and the other students who showed difficulty with the teen number last week.

"I notice that the 17 is also missing.  What do you think happened to it?"

Without hesitation, she grabbed the 10 and 7 and made 17.  She said "10 plus 7 equals 17"

I asked her to sit down and quizzed a few more selected students on what happened to the other teen numbers.  They did amazing.  I will follow up with more formative assessment later this week, but I think they all got it now!  

Apparently today, the kids knew better than I did what they needed to learn next. 

Have you ever had a lesson go completely off track but really help your students' understanding?