Over the last decade, much of my work has been focused on mathematical argument in the elementary classroom. Observing in our collaborating classrooms, I was struck again and again by how teachers supported students to build on each other’s incomplete ideas. Constructing a mathematical argument is difficult and challenging for elementary students and, therefore, necessarily collaborative.

When students are learning what it means to make an argument, not just about the solution to a single problem, but about something that’s generally true in mathematics, they start out by noticing a regularity across multiple examples. In this fourth-grade class, the teacher posts four pairs of equations that are examples of something that’s true about addition. She deliberately chooses addition problems that are easy for the fourth graders because the focus in this lesson is not about solving the problems but about how the operation of addition behaves, no matter what the numbers are.

In the following excerpt from their conversation, the teacher engages her students in articulating what they notice, and encourages them to do the hard work of finding words that clearly describe the common mathematical structure underlying these pairs of equations. She doesn’t expect any one student to formulate a clear and precise conjecture. Rather, she repeatedly invites students to restate and add to the evolving idea.

Teacher: We’re going to try to look at what’s happening with these numbers. We’re going to look for some patterns, and we’re going to make a guess, a conjecture, about what we think is going to be true for all numbers that have these patterns. What do you notice?

Martina [pointing to the first pair of equations]: I’m saying, in the first column [pointing to the 12 and 14 in the first pair of equations], it goes up by two. In the second column [pointing to the two 8’s], it doesn’t go up by anything because it’s the same number, so the answer has to go up by two.

Teacher: Okay, who can explain it in a different way?

Ana Sofía: These numbers [points to 12 and 14] are changing by two, but the second column, the numbers stay the same, so you know that the last digit [points to the sum] is going to have a difference by two.

Several students: Oooh!!

Teacher: Okay, Kevin, can you say it in a different way?

Kevin: Well, what I was basically saying is… I’m just saying that this basically grew. This one grew two more, so the sum from here to here would just grow two more because you added two on…

The teacher asks students to turn and talk in pairs about what they’re understanding and whether they can state a rule. Then the discussion continues.

Isabella: …the rules for the twos, I got — well like he was saying that, you’re adding the two because, um…

Isabella drifts off and stops. The teacher asks her if she wants to call on someone else to add on to what she started. She calls on Nicole.

Nicole: Well, I think Kevin’s rule with the two’s is that, you just basically—if you answer— Well, if the first or second addend— So, if you have a problem, like 12 + 8 = 20, and then you write another problem down, like 14 + 8 = 22, and then the only— I think Kevin was saying that since 2 + 2 = 4, then basically—  wait, I don’t know what I’m talking about. Two more would be 4, and then the answer has to be two more.

Teacher: So, let’s take that part of yours, “the answer has to be two more.” Why does it have to be two more? Who can add on to make a short rule about what Nicole was saying?

Anthony: So, what’s happening is, if you add two to one of the addends, the answer has to be two more.

In this excerpt, Martina gets out some important ideas, but only when Ana Sofía re-states those ideas do some students begin to follow. They needed time, and more than one chance to hear the ideas, to think them through. Kevin introduces the word sum and explicitly connects the change in the sum to the change in an addend. Nicole picks up on this connection: “the answer has to be two more.” Anthony articulates a concise rule that has the essence of all these ideas. And even this is not the end of that day’s conversation—but all I have space to quote here!

Through this discussion, students’ articulation of their collective idea gradually becomes clearer and more precise. The invitation to start and stop, to be inarticulate, to get out a partial thought, even to be incorrect, results in a gradual refining and increased understanding of the mathematical idea. This invitation not to have to be right—now taken for granted in this classroom, but only after a lot of work to establish this expectation—signals that all ideas help move the collaborative effort of understanding mathematics forward. It allows all students to participate and their collective brilliance to be developed and shared.


This example is taken from But Why Does It Work: Mathematical Argument in the Elementary Classroom by Susan Jo Russell, Deborah Schifter, Reva Kasman, Virginia Bastable, and Traci Higgins. Heinemann, 2017.

Susan Jo Russell

Susan Jo Russell

Susan Jo began her career in education as an elementary classroom teacher and math coach. She co-directed the original development and second edition of Investigations in Number, Data and Space. Her research has focused on children’s mathematical understanding and on how teachers can learn more about mathematics and about children's mathematical thinking. Current work centers on early algebra, number and operations, mathematical argument, and how teachers can support students to engage in mathematical practices.
Susan Jo Russell

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Tag(s): addition | classroom culture | grade 4 | making sense | mathematical argument |