Monday, December 5, 2016

Down the Rounding Rabbit Hole


     Rounding has always been difficult for me to teach, and I suspect I'm not alone.  Here's a look at some of the many gimmicks, tricks, and tools teachers have used in an effort to get this concept across:


Been there.


Done that.

Looks familiar.

Monkeys?  Can't say I've ever tried this, but I'm skeptical.



Not sure what this is.


Seems like a lot to process, and I'll admit I've said similar things.

     Our curriculum likes number lines:

Grade 3

Grade 3 again.  Not a mountain or a roller coaster...it's a hill!


Grade 4

     I've spent more time than usual this fall thinking about rounding; both the why and the when, but also simply the how.  Using a number line to round is all well and good, but it's not going to help you solve these problems...




...unless you can do the following:
  • Identify place value locations and the value of the digit in a given place value.
  • Identify the next multiple in that place value.
  • Find the halfway point between the two multiples to use as a benchmark.
  • Decide whether the number is more or less than halfway.     
That's one big cognitive load.  No wonder many kids struggle!

    Last year, I tried something different with some third graders who were having difficulty with rounding.  Here's a typical problem from their journal:

An open number line won't help unless you know the multiplies of 10 that come before and after 68.


Start with 68.


Count forward by 1s until you get to a number you would say if you skip counted by 10s.

Same, but this time count backwards.


Find out if 68 is closer to 60 or 70.  This also reinforces complements of 10.


    This was good as far as it went, but to round larger numbers, especially to units represented by a place in the middle of that number, students will need another strategy, hopefully one that doesn't rely on mountains, roller coasters, digits knocking on doors, or monkeys swinging on vines.
     This fall I've been working with a fourth grader who, at the beginning of the school year, showed a complete inability to round.  She had a very limited notion of place value, and we spent several weeks shoring up some basics.

We used this flip board...


...and these place value arrow cards.


   I wanted her to be secure in her knowledge of place value locations and digit values before we ventured off into the world of rounding.  It took several weeks, but once she was able to complete tasks like this:




and this:


without the board or the arrow cards, I moved her on to rounding.  Here's the plan I had sketched out.  Let's take a grade 4 example.  Round 81,866 to the nearest thousand:

Step 1: Write the number out in expanded notation.

 
Step 2: Identify the place value you want to round to.


Step 3: Identify the next multiple in that place value.  Here I might say something like, "If I was skip counting by thousands, what number would come after 1,000?"

Step 4: Put the 80,000 back.  This can be combined with step 3.

Step 5: Now we're ready for our number line.  We have our two possible responses for rounding 81,866 to the nearest thousand, so now we've got a fighting chance.


Step 6: Where does 81,866 fall on this number line?  Can we benchmark halfway?

  
Step 7:  This is now a matter of comparing 500 and 866.

We practiced on the big whiteboard in my room, and experimented with color:

Rounding 697,654 to the nearest thousand.  After a while, she started to internalize some of the steps.


Here's an example of the student employing the strategy in her math notebook:

Rounding 818,325 to the nearest thousand.  I would've liked to see her place the mark for 818,325 closer to 818,500, but that's for another day.



     I'm happy to report that she's made lots of progress.  The mistakes she makes when rounding now come when she tries to do too much in her head.  Soon she will be able to visualize the number line in her mind's eye; the two boundaries, the halfway mark, the place where the number belongs.  Soon, but not yet.
     So here's what I found out: 4.NBT.A.3 is a very interesting standard.

   

    It's stated so simply, and, compared to others, seems so uncomplicated.  But my dive into rounding this fall taught me that there's much more here than meets the eye.  Place value understanding is a complex understanding with many components, and all of them have to be secure and working in concert in order for students to be able to round multi-digit whole numbers to any place.
    As I continued to work with the student, the nagging question of why are we doing this kept running through my mind.  Curious to learn more, I found this on page 12 of the Numbers and Operations in Base Ten, K-5 progressions document:

Rounding to the unit represented by the leftmost place is typically the sort of estimate that is easiest for students and is often sufficient for practical purposes.  Rounding to the unit represented by a place in the middle of a number may be more difficult for students (the surrounding digits are sometimes distracting).  Rounding two numbers before computing can take as long as just computing their sum or difference.  (emphasis mine)

Here's what I want to know:
  • If rounding to the unit represented by the leftmost place is often sufficient for practical purposes, then why are we asking students to round, for example, 287,347 to the nearest hundred?  What headache do I have that rounding 287,347 to the nearest hundred will cure?
  • Are tasks asking students to round numbers to units represented by places in the middle of a number simply exercises in place value?  Is there a way to make this task compelling?     
  • What distinctions do the progressions make between rounding and estimating?  
  • Should rounding be taught as a discrete skill, separate from any context?  
  • What scaffolds, tools, and place value models are helpful in promoting rounding understanding, and which subvert it?
And finally: What are your experiences teaching rounding?







Tuesday, November 22, 2016

More Faculty Lounge Math

     My teaching life pre-MTBoS was certainly different than it is now.  I look at student work differentlyplan lessons and activities differentlyprovide feedback differently, even think of myself as a math learner in a different way than I did before becoming an active part of this amazing community.  But nothing has changed more than the way I look at what I see around me.  My friend Graham Fletcher has taught me that what I'm doing is called mathematizing the world, and now that I've started, I can't seem to stop.  In that spirit, here's another edition of Faculty Lounge Math.

Pretzels
     This is more like a 2-Act than a 3-Act...


What fraction of the container is filled with pretzels?




Does this help?



Muffins
  This one got tweeted out:










Rainbow Cookie


Fractions anyone?



A Faculty Lounge 3-Act

Act 1




Washing Up from Joe Schwartz on Vimeo.

Main Question: How many squirts will the machine dispense until it runs out of soap?



Act 2

Inside.  According to the company, 0.4 mL of liquid foam soap is dispensed each time it's activated.

The dispenser holds 1 bag.  Each bag holds 1,200 mL of foam soap.  
Act 3

  My first attempt at figuring this out didn't go so good.

I added 3 + 10 + 100.  I don't know... 113 handwashings just seemed too low.


So I tried something different...

3,000 was more like it!

Where did I go wrong?

Thinking additively, not multiplicatively.



 Act 4: The Sequel
 
The dispenser can be set to squirt 0.7 mL of soap per activation.  How many hand washings per bag?

   A jar of pretzels, trays of muffins, a cookie, a soap dispenser; in my previous life they would have been things to eat and a way to promote good hygiene.  But thanks to DanAndrewGrahamMarilynRobertTraceyMichaelSimonKristinFawnMax,  Annie, Andy, and the rest of the MTBoS crew, I now see them as opportunities to notice and wonder, estimate, spark a number talk, and create and solve problems.  It's a gift I'm thankful for.  Hope they don't mind if I re-gift.


Monday, November 7, 2016

Two New Routines

Courtesy of Sarah Carter, a pair of high yield geometry routines I experimented with last month with our fifth graders:

Quick Build

     I flashed this image on the SmartBoard for a few seconds, then took it down:


  Using snap cubes, students had to build the structure from memory:



It's OK to show it a second and even a third time.  



     After all had built the structure, I asked them to share how they had visualized it in their minds, and their responses were quite varied.  Some saw a 2 by 3 rectangular prism with a two-step staircase attached, others saw a three-step staircase with a 1 by 3 rectangular prism attached.  Still others saw 3 levels: 4 on the bottom, 3 in the middle, and 2 on the top.
     Then I asked about the structure's volume, and they generated lots of equations:

AM class

PM class

I liked this activity for several reasons:
  • It reinforced the idea of finding the volume of non-overlapping right rectangular prisms, which is a major grade 5 focus.
  • It reinforced order of operations and writing equations, another grade 5 standard.
  • It inspired a little number talk.
Also, the kids loved it!  They want to do it again, but next time with, as one student put it, "Harder shapes."  So I have this one loaded up:


Quick Draw

     This activity comes from Grayson Wheatley.  Again, flash the image for a few seconds, then take it down.  Ask kids to draw the figure from memory.  

I chose this one for our first try.

One student's effort:


quick draw video from Joe Schwartz on Vimeo.

Another:



     As with quick build, I asked the kids how they visualized:
  • "A square, with a box around it, with 4 trapezoids."
  • "A box in a box with 4 lines connecting the corners."
  • "A  3-D cube facing me."
  • "A room with a ceiling, two walls, and a floor."
  • "A pyramid with the top cut off."
Lots of great vocabulary was generated:

Parallel and intersecting lines, right, acute, and obtuse angles, corners, sides, 2- and 3- dimensional shape names...what's not to like?


     Number talks, counting circles, estimation180, subitizing; we've done a good job infusing these routines into our instructional practice.  That's a balance weighted heavily on the number sense side. These two routines, which emphasize spatial reasoning and geometry, are a needed and important counterweight, and I look forward to more experimentation across grades K-5.  And again, thanks to Math = Love for the inspiration!

Thursday, October 27, 2016

Frowny Face

   I feel Brian's pain.  There are few things worse than being undermined by a poorly designed worksheet.  This one popped up in a grade 4 class last month, in the middle of a unit on rounding:

This worksheet had 10 word problems on it.  I'm not sure why you would want to estimate; the questions appear to call for precise answers.  And why to the nearest ten?

     As I was walking around the room, looking at student work and helping those with questions, I could feel my anger rising.  "Here we go again," I thought.  Until something on one student's paper caught my eye:

A small frowny face.
     I knelt down by her desk.
     "Why the sad face?" I asked.
     "I don't like this problem," she responded.
     "Why not?"
     "Well, when I round each of those numbers to the nearest ten, I get 540 and 250.  Those are not so easy for me to subtract."
      "What would make things easier for you?"
      "I could round the 536 to 500 and the 246 to 200 and just subtract 500 - 200 and get 300.  That's easy for me because I know that 5 - 2 = 3."
     "Then you go right ahead and do that!" I told her.
     "But the directions say to round each number to the nearest tens!"  She was nervous that the teacher might mark it wrong.
     "That's OK," I assured her.  "I'll talk with her."

Her answer.  Unit issues aside, isn't it better than two question marks?

     Worksheets like these, in which problems exist for the sole purpose of having kids practice a skill, fail on several levels.  They poorly serve the concept they're designed to reinforce (rounding), and they force kids into a single way of thinking (to the nearest ten.)
     This student knew there was something wrong.  She expressed her displeasure in the only way she knew how: by drawing a frowny face.  I love that frowny face!   Keep 'em coming, kids!