Category Archives: Talking math with your kids

Standard algorithms unteach place value

I found a page full of computations sitting around the house this evening. Naturally, I picked it up and gave it a look.

Griffin (10 years old, 5th grade) had been doing some multiplication in class today. Somehow his scratch paper ended up on our couch.

Here is one thing I saw.

37 times 22 with the standard algorithm. Wrong answer: 202.

Naturally I wanted to ask the boy about it. He consented.

Me: I see you were multiplying 37 by 22 here.

Griffin (10 years old): Yeah. But I got it wrong so I did it again with the lattice.

Me: How did you know you got it wrong?

G: I put it in the answer box and it was wrong.

It turns out they were doing some online exercises. There is an electronic scratchpad, which he found awkward to use with a mouse (duh), plus his teacher wanted to be able to see their work, so was encouraging paper and pencil work anyway.

I was really hoping he would say that 37 times 22 has to be a lot bigger than 202. Alas he did not.

Anyway, back to the conversation.

Me: OK. Now 37 times 2 isn’t 101. But let’s imagine that’s right for now. We’ll come back to that.

G: Wait. That’s supposed to be 37 times 2? I though you just multiplied that by that, and that by that.

He indicated 7 times 2, and then 3 times the same 2 as he spoke.

Me: Yes. But when you do that, you’ll get the same thing as 37 times 2.

A brief moment of silence hung between us.

Me: What is 37 times 2?

G: Well….74.

Let us pause to reflect here.

This boy can think about numbers. He got 37 times 2 faster in his head than I would have with pencil and paper. But when he uses the standard algorithm that all goes out the window in favor of the steps.

THE STEPS WIN, PEOPLE!

The steps trump thinking. The steps trump number sense.

The steps triumph over all.

Back to the conversation.

Me: Yes. 74. Good. I like that you thought that out. Let’s go back to imagining that 101 is right for a moment. Then the next thing you did was multiply 37 by this 2, right?

I gestured to the 2 in the tens place.

G: Yes.

Me: But that’s not really a 2.

G: Oh. Yeah.

Me: That’s a 20. Two tens.

G: Yeah.

Me: So it would be 101 tens.

G: Yeah.

I know this reads like I was dragging him through the line of reasoning, but I assure you that this is ground he knows well. I leading him along a well known path that he didn’t realize he was on, not dragging him trailing behind me through new territory. We had other things to discuss. Bedtime was approaching. We needed to move on.

Me: Now. We both know that 37 times 2 isn’t 101. Let’s look at how that goes. You multiplied 7 by 2, right?

G: Yup. That’s 14.

Me: So you write the 4 and carry the 1.

G: That’s what I did.

Me: mmmm?

G: Oh. I wrote the one

Me: and carried the 4. Yeah. If you had done it the other way around, you’d have the 4 there [indicating the units place], and then 3 times 2 plus 1.

G: Seven.

Me: Yeah. So there’s your 74.

This place value error was consistent in his work on this page.

Let me be clear: this error will be easy to fix. I have no fears that my boy will be unable to multiply in his adolescence or adult life. Indeed, once he knew that he had wrong answers (because the computer told him so), he went back to his favorite algorithm—the lattice—and got correct answers.

I am not worried about this boy. He is and he will be fine.

But I want to point out…I need to point out that this is exactly the outcome you should expect when you go about teaching standard algorithms.

If you wonder why your kids (whether your offspring, your students, or both) are not thinking about the math they are doing, it is because the algorithms we (you) teach them are designed so that people do not have to think. That is why they are efficient.

If you want kids who get right answers without thinking, then go ahead and keep focusing on those steps. Griffin gets right answer with the lattice algorithm, and I have every confidence that I can train him to get right answers with the standard algorithm too.

But we should not kid ourselves that we are teaching mathematical thinking along the way. Griffin turned off part of his brain (the part that gets 37 times 2 quickly) in order to follow a set of steps that didn’t make sense to him.

And we shouldn’t kid ourselves that this is only an issue in the elementary grades when kids are learning arithmetic.

Algebra. The quadratic formula is an algorithm. Every algebra student memorizes it. How it relates to inverses, though? Totally obfuscated. See, we don’t have kids find inverses of quadratics because those inverses are not functions; they are relations. If we did have kids find inverses of quadratics, they could think about the relationship between the quadratic formula:

x=\frac{-b \pm \sqrt{b^2-4ac}}{2a}

and the formula for the inverse relation of the general form of a quadratic:

y=\frac{-b \pm \sqrt{b^2-4ac+4ax}}{2a}

Calculus. So many formulas (algorithms) that force students not to think about the underlying relationships. If we wanted students to really think about rates of change (which are what Calculus is really about), we might have them develop a theory of secant lines and finite differences before we do limits and tangent lines. We might have Calculus students do tasks such as Sweet Tooth from Mathalicious (free throughout October!). There, students think about marginal enjoyment and total enjoyment.

On and on.

This is pervasive in mathematics teaching.

The results are mistaken for the content.

So we teach kids to get results. And we inadvertently teach them not to use what they know about the content—not to look for new things to know. Not to question or wonder or connect.

I’m telling you, though, that it doesn’t have to be this way.

Consider the case of Talking Math with Your Kids. There we have reports from around the country of parents and children talking about the ideas of mathematics, not the procedures.

Consider the case of Kristin (@MathMinds on Twitter), a fifth grade teacher, and her student “Billy”. Billy made an unusual claim about even and odd numbers. She followed up, she shared, we discussed on Twitter. Pretty soon, teachers around the country were engaged in thinking about whether Billy would call 3.0 even or odd.

But standard algorithms don’t teach any of that. They teach children to get answers. They teach children not to think.

I have read about it. I have thought about it. And tonight I saw it in my very own home.

The latest “Common Core” worksheet

You have seen this on Facebook.

Original (Click to enlarge)

Ugh what a mess.

Please share the annotated version widely.

I’ll say what I have to say (comments closed) and move on. If you wish to discuss further, hit me up on Twitter or pingback to the blog. Want to talk in private? Click the About/Contact link up top.

Also, Justin Aion—middle school teacher extraordinaire—wrote up his views on the matter. You can read them over in his house.

Here goes…

The intended answer

Dear Jack,

You only subtracted 306 from 427, not 316. You need to subtract another 10 to get the correct answer of 111.

Sincerely,

Helpful student

The purpose of this task

I cannot say whether this was the right task for this child at this time because I do not know the child, the teacher or the classroom.

I can say the following:

  • Analyzing errors is a useful way to encourage metacognition, which means thinking about your thinking. This is an important part of training our minds.
  • The number line here is a representation of a certain kind of thinking—counting back. The number line is not the algorithm. The number line records Jack’s thinking. He counted back from 427 by hundreds. Then he counted back by ones. He skipped the tens. We can see this error because he recorded his thinking with a number line.
  • Coincidentally, the calculation in question requires no regrouping (borrowing) in the standard algorithm, so the problem appears deceptively simple in its simplified version.
  • This task is intended to help students connect the steps of the standard (simplified) algorithm with reasoning that is based on the values of the numbers involved. Why count back by three big jumps? Because you are subtracting 300-something. Why count back by six small jumps? Because you are subtracting something-something-6. Wait! What happened to the 1 in the tens place? Oops. Jack forgot it. That’s his mistake.

So what?

The Common Core State Standards do require students to use number lines more than is common practice in many present elementary curricula. When well executed, these number lines provide support for kids to express their mental math strategies.

No one is advocating that children need to draw a number line to compute multi-digit subtraction problems that they can quickly execute in other ways.

The Common Core State Standards dictate teaching the standard algorithms for all four arithmetic operations.

But the “Frustrated Parent” who signed that letter, and the many people with whom that letter resonated, seem not to understand that they themselves think the way Jack is trying to in this task.

Here is the test of that.

A task

What is 1001 minus 2?

You had better not be getting out paper and pencil for this. As an adult “with extensive study in differential equations,” you had better be able to do it as quickly as my 9-year old.

He knows with certainty that 1001 minus 2 is 999. But he does not know how to get the algorithm to make that happen.

If I have to choose one of those two—(1) Know the correct answer with certainty based on the values of the numbers involved, and (2) Get the correct answer using a particular algorithm, but needing paper and pencil to solve this and similar problems—I choose (1) every time.

But we don’t have to choose. We need to work on both.

That’s not Common Core.

That’s common sense.

[Comments closed]

An interesting story about research and assumptions

Nature v. nurture. Age-old debate on relative importance. Not gonna settle it here. Not even in the limited context of factors influencing mathematics success.

There is lots of interesting research going on, of course. I want to tell you a quick story about a very small subset of that research.

A few years back, a group of educational psychology researchers published a study that phys.org headlined, “Math ability is inborn“.

The study investigated the ability of 4-year olds to choose the larger of two sets of dots when these sets were viewed briefly (too briefly to allow for counting).

They found that children who were better at this task also knew more about numeration and counting.

A quote from one of the researchers, Melissa Libertus:

“Previous studies testing older children left open the possibility that differences in instructional experience is what caused the difference in their number sense; in other words, that some children tested in middle or high school looked like they had better number sense simply because they had had better math instruction. Unlike those studies, this one shows that the link between ‘number sense’ and math ability is already present before the beginning of formal math instruction.”

Read more at: http://phys.org/news/2011-08-math-ability-inborn.html#jCp

Let’s pause for a moment to think, shall we?

If a child has not had formal instruction in mathematics, is the only remaining possibility that her mathematical performance is due to innate skill?

Of course it isn’t.

There is also the possibility that the child has absorbed some mathematical knowledge from her environment, and that different environments might provide differential input.

Maybe the child who is better at discerning the larger set has more practice doing just that. Maybe that child’s parents have been asking her how many? how much? and which is more? for the last two or three years.

Maybe that child’s parents have been Talking Math with Their Kids.

Mindsets, research and talking math with kids [#NYTEdTech]

This conversation happened in New York yesterday.

A view of New York City from the Times Center on Tuesday.

A view of New York City from the Times Center on Tuesday.

During a coffee break, I sat down on a white pleather sofa next to an older man.

Me: How has your day been?

Him: Good. You?

Me: Pretty good. Interesting.

What do you do?

Him: Retired.

Me: From what?

Him: I was president of [small New England college]. How about yourself?

Me: I teach math at a community college in Minnesota.

But I’m also working on a project. I work with future elementary teachers, so I have studied the mathematical development of children.

Him: Uh huh.

Me: And I want to use that knowledge for something else, which is this: I am trying to understand what knowledge parents need in order to support the mathematical development of their children.

Him: That’s important.

Me: Right.

[Short pause]

Me: Do you have grandchildren?

Him: Yes. They are 8 and 10.

Me: Oh nice! So their parents—your kids—are my target market.

Him: Yes. Their father is really into that. They use Khan Academy and all that.

—FIN—

If the end of that conversation makes no sense to you, I ask that you please, please, please spend the next 15 minutes over at my website, Talking Math with Your Kids. You might be especially interested in the research summaries, which demonstrate that young children need to talk about number and shape with their parents rather than (or at least in addition to) being sent to website, iPad apps and decks of flash cards.

Kids need mathematical conversation. And they enjoy it.

Talking Math with Your Kids for Kindle!

Someday there will be a full-sized paper version of a Talking Math with Your Kids book (Hear that publishers? Wanna talk? You can find me at the About/Contact page.)

Until that day, there is now a mini-version (15,000 words; roughly three chapters, $4.99) available on Kindle (and readable on other devices with the Kindle app).

Tabitha is delighted by the news!

Tabitha is delighted by the news!

Go have a look, won’t you? Share widely and let me know what you think.

Table of contents:

  1. Introduction
  2. Counting and other adventures in number language
  3. Adding and subtracting: Two peas in a pod
  4. Conclusion
  5. References and further reading

The book is structured around conversations I have had with Griffin and Tabitha. About 1/3 of the conversations in the book have been previously documented here and/or on the new Talking Math with Your Kids site. The rest are new to readers.

There is lots of new content summarizing research in parent-friendly ways.

The impetus for getting this out now is this: funding my New York Times Schools for Tomorrow trip. I got partial funding from my college, but it’s an expensive conference. So I hacked a couple of chapters out of a draft I have been working on for quite a while now, tidied and edited them and voilá!

Griffin and Tabitha are moving

omt.moving

For two years now, I have been documenting the mathematical conversations we have around the house, filed under the category, “Talking Math with Your Kids”.

I have long wanted to bring these conversations to the attention of non-mathy parents. But seriously, they want to wade through my musings on College Algebra, elementary teacher preparation and Khan Academy? I don’t think so.

So these conversations are moving.

To talkingmathwithkids.com

Come join us over there, won’t you?

More importantly, do us the favor of sharing the link with parents and caregivers of your favorite 0—10 year olds. Especially those who might be a little bit afraid of math.

In writing for parents, I’m fleshing out the conversations with information about kids’ mathematical development, and with ideas for starting similar conversations with their own kids.

We’ll review products that are targeted at kids and math, and share relevant research and news.

There’s even a contact page where parents can report conversations they have with their kids, and ask questions.

We’re just getting started, so give us a hand won’t you?

 

The oldest man in the world

Tabitha (six years old) and Griffin (on the cusp of nine) are attending a three-hour soccer camp in the neighborhood every afternoon this week. Furthermore, she has been begging to come to Tuesday night Ultimate Frisbee with me this summer. This week was the first opportunity for her to come along. It’s about a half hour ride up to Blaine so we had time to chat in the car.

Tabitha (6 years old): My group is 6 and under, but everyone is 6.

Me: Interesting.

T: Yeah. Six and under, so even a zero-year-old could play.

Me: I suppose so. But everyone is six, so there are no “unders”.

T: Daddy, everyone is under something.

Me: Huh?

T: Like you. You’re under 100.

Me: I suppose so. But then everyone you know is under 100.

T: Not the famous guy.

Me: What famous guy?

T: The oldest man in the world. He’s not under 100.

Me: No he’s not. But you don’t know him either.

T: Yes I do. I read about him in a book.

Feeling smug for having won this round, Tabitha sits in silence for a moment.

T: Are his mom and dad still alive?

Me: Whose mom and dad?

T: The oldest man in the world.

Me: Let’s see if you can work this out yourself.

T: Oh! They’re not alive.

Me: How do you know?

T: Well, his mom and dad are older than him. So if they were alive, they would be the oldest people in the world.

Pause.

T: Or, they could be alive, but younger than him.

Postscript

Quick plug: Tony Sanneh is evidently from Minnesota. He has a foundation that, among other things, offers free soccer camps in Minneapolis and St Paul recreation centers. They seem to be really positive, well run affairs drawing kids of diverse economic and cultural backgrounds. From what I can tell, they are doing lovely work that we should applaud.