Fractions Number & Operations -- Fractions Numbers & Operations -- Fractions

2/3 as a “2 by 3”

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When kids are learning to give fractions meaning, I think they often struggle to figure out how the numerator and denominator are coordinated. Here we see a middle step in understanding, maybe: it’s not that the numerator and denominator are totally disconnected. They’re just coordinated in a way that doesn’t really correspond to how they actually work together (i.e. denominator tells you the “unit” and the numerator tells you the “quantity.”)

Maybe the progression of learning looks like this:

  • 2/3 means “2 and 3,” nothing to do with each other. Totally baffling notation.
  • 2/3 means “2 by 3” or “2 times 3,” some more familiar situation where two numbers can be coordinated in a relation.
  • 2/3 means “2 thirds,” which is a productive way to coordinate the numerator and denominator.

Thoughts? Am I overinterpreting this as a middle step in a progression, when it’s actually just a totally uncoordinated interpretation of the fraction?

Fractions Fractions Grade 4 Numbers & Operations -- Fractions

Which Mistake Most Surprises You?

Fraction comparison for 4th Graders. They’ve been working a lot with representing fractions as circles and as rectangles. They’ve done some basic addition with fractions. Most aren’t generally able to find equivalent fractions.


What mistakes do you expect to see in the class set?

Make a prediction! Mark it down somewhere. Don’t do that internet thing of just continuously scrolling through a page at half-attention. Take a moment, form a thought. Then scroll on for the full class set of 14.

In the comments, would you please answer this question: Which mistake most surprised you? Why?

Kid 1

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Kid 2

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Kid 3

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Kid 4

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Kid 5

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Kid 6

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Kid 7

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Kid 8

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Kid 9

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Kid 10

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Kid 11

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Kid 12

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Kid 13

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Kid 14 

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Decimals Numbers & Operations -- Fractions

We have no idea whether 0.1 is 1/10 or 1/100.

I put “0.1” on the board and asked students what they’d call this. A kid said “one tenth,” but that quickly became controversial.

Question: how do you think these kids are seeing 0.1?

Fractions Numbers & Operations -- Fractions

Three Fifths of a Triangle

Three fifths triangle


Shared by Tracy on twitter, and a great conversation ensued.

Fractions Numbers & Operations -- Fractions

Andrew Stadel’s Black Box // Adding Fractions

I’m a big fan of Stadel’s Black Box. I think what makes it fun is that there’s something small to figure out (What does the black box do?) before figuring out the big thing (What’s the sum of those two fractions?)



I recently did this with my fourth graders, and it was a ton of fun. Here were some of their answers to 1/2 + 1/3:


3 1/2 / 4  (three and a half fourths)





Can you figure out how kids got each of these answers?

Fractions Grade 4 Numbers & Operations -- Fractions

3 and a half fourths

adding2 Adding3 Adding1


Not really a mistake, but my kids have started doing this.

How do we feel about this, team? I think that I like it.

Fractions Grade 4 Numbers & Operations -- Fractions

Fraction bar as an operation

Misconceptions surrounding fractions are so well-studied that I feel a bit ridiculous sharing anything about them. Anyway…

I was chatting with this kid who was having a bunch of trouble with written fraction notation. She had been correctly solving problems that involved language such as “shade in four out of seven pieces” or “divide this shape into eighths,” but got stuck when she reached a problem that asked her to “shade in 4/6 of the shape.”

Alice: Oh, so that’s 5.

Me: Can you explain why?

Alice: Because it’s not six sixths.

Me: So, not quite.

Alice: Oh, it’s 2. Because that’s 6-4.


Alice: Or it’s 10?

Me: See…

Alice: I’m really confused here. What’s the answer?

There’s no puzzles or misunderstandings here. Alice thought that the fraction symbol was an operation between the numbers 4 and 6. And of course she did. Every other time that she’s seen two numbers and a symbol before she’s been asked to produce a third number. This is new ground for her.

I’ve been taking the advice of Brilliant Commenters Fawn, Jenny and Avery and using the language of “out of” to bridge the gap for this kid.


Decimals Fractions Numbers & Operations -- Fractions

A 4th Grader Who Prefers Decimals to Fractions



This student — let’s call her Alice — is in 4th Grade. She did some work with fractions in 3rd Grade, but clearly isn’t comfortable with them.

I went over to Alice and noticed that she wrote “0.5” for point A. I asked her to read that number, and she said “a half.” Then I drew a half-filled circle and I asked Alice to tell me what fraction of the circle was filled in. She said “a half.”

Me: Can you write “a half” as a fraction?

Alice: Why do you have to? This way is so much easier.

[I show her how I write a half.]

Alice: Oh, a one and a two.

[I draw two more circles, one with a quarter filled in, the other with three quarters filled in.]

Me: What part of the circle is filled in in these two circles?

Alice: A quarter. Three quarters.

Me: How would you write those numbers down.

Alice: Umm…so this would be one-four?

Me: Yes, though I’d read this as one-fourth.

Alice: And this would be one-three.

This is interesting in all sorts of ways. First, because you can really see in Alice’s work the difference between written and spoken language. Alice can tell you what a half is. She can even tell you how much is shaded in on the other circles, but she can’t write it. Attention needs to be given to both verbal and written language, and we teachers tend to focus on our students written work.

Also, “one-four” and “one-three”? That’s so interesting. Alice sees “three” as the most important part of “three quarters,” and tentatively thinks that fractions are just always “one-something.” That’s a pretty strong tell.

The other remarkable thing is how strongly Alice prefers decimal representations to fractions. Alice showed this preference consistently in her problem solving.



The kindly Professor Danielson argues that, in a curriculum, fractions ought to precede decimals. But it’s also true that decimals are addictive. In my high school classes, kids use their calculators to transform fractions to decimals as a defensive measure. You know the easiest way to help (most) kids solve equations with fractions? Point out that they can convert those fractions to decimals.

Decimals are absolutely enticing to people, even to this kid who is just getting started in this whole mess.

Decimals Division Fractions Numbers & Operations -- Fractions Numbers & Operations in Base 10

44 crackers shared equally with 8 people…



Lots of good stuff going on here. But I don’t think I entirely understand where 1/8 came from, though I get how that gets turned into 5.8.











[I never know whether to include all the mistakes from a class set or just a few. I feel as if it’s helpful to include more mistakes, but sometimes overwhelming. My solution today is to post one especially cool mistake largely, and the others smallerly. Let me know whether that works.]

Decimals Fractions Numbers & Operations -- Fractions

Plot 0.4 on the Number Line



How did the student make the decision to plot 1/4? Tell a story.

Source: Chris Robinson