Series: Math Routines with Kristin Gray: Second Grade


Common core State Standards

  • Math:  Math
  • 2:  Grade 2
  • NBT:  Number & Operations in Base Ten
  • B:  Use place value understanding and properties of operations to add and subtract
  • 5: 
    Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.

Download Common Core State Standards (PDF 1.2 MB)

Subtraction Number String: Second Grade
Grade 2 / Math / Tch DIY

A number string is a series of mathematical expressions organized in a way that encourages students to build on their thinking as the string progresses.

Thank you for putting up these videos. These ideas i incorporate in my programme as warm up activities for classroom discourse.
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I love this quick lesson on number relationships. Grasping the concept of subtracting more or less will produce an answer that is less or more can be difficult for young students.
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Hi, Kristin! I wanted to let you know (publicly, in this space) and others know that I am finding your Number Talk / number string videos helpful to use when teaching elementary mathematics methods to future teachers. Specifically, one aspect that was useful was your reflection question at the end. Many of my pre-service teachers wonder what the students who were NOT talking were thinking about during a number talk -- your example of asking students to reflect individually at the end of a Number Talk is a good way to address this wonderment. Additionally, the reflection question that you posed to the students -- design a new number string that is similar to the number string in the video -- was not only useful for your students, but it was useful for my future teachers (and me!). One challenge that future teachers have is designing a number string for a number talk -- thinking about the goals for their students and how the number string's design helps students progress toward these goals. I gave the same reflection question to my future teachers during the methods course after we discussed this video! One interesting option was changing the minuend rather than the subtrahend. For instance, a pre-service teacher wrote one pair as 70 - 30 and 73 - 30. She wrote that you changed the subtrahend, but never the minuend, so next I am curious as to how changing the minuend would affect students' thinking. So in this case, instead of designing a number string aligned with the goals of this video, she designed a slightly different number string and articulated a new goal -- as if thinking about a next type of number string -- what would come next for these students? Cool thinking on her part. Another interesting variation was starting with the recalled fact related to 25s, like 100 - 25 and 100 - 27, rather than recalled facts as two tens (such as 100 - 30). Anyhow, just sharing a few thoughts and appreciating the work that went into these videos! I wanted you to know that I am putting them to use at the University of Delaware. A larger goal I have is to let these future teachers know that the Teaching Channel is a helpful resource for professional learning.
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Thank you so much Mandy! It is so great to hear how the videos are being used so specifically and the conversations they inspired. I love all of the ideas that came after the video! I think your work in discussion about the design is invaluable and one of my favorite parts of working with teachers around Number Talks. The questions, "What happens if we do this instead of that? or What happens if we use this number over that number?" get so much into both the mathematics and how students develop a thought process around them. I love the discussion about changing the subtrahend vs the minuend. The powerful thing about number talks is the ability to explicitly plan toward a specific thought process or strategy. Since subtraction is the bane of every grade levels' number talks, even in my own 5th grade class, I wanted to address two things that come up often across grades: 1- the "borrowing" the teacher was seeing students do and 2 - understanding we end with less if we take away more from the same number, hence the same minuend and changing subtrahend. I really wanted them to make sense of the answer because when they would try to borrow for a problem like 90 - 61, they would get 31 by lining up and subtracting by place, never thinking that it didn't make sense to end with more than 90-60. I love the question of the "next move" and where to go from here. I always struggle with how much time to spend on one idea before moving onto another such as changing the minuend. Keep all of the reflections coming and I would love to visit your class sometime!
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One thing I liked in addition to the math talk was that you gave plenty of wait time. I also like the "I agree" hand signal, which I think is like hang loose in Hawaii!
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School Details

Shields (Richard A.) Elementary School
910 Shields Avenue
Lewes DE 19958
Population: 707

Data Provided By:



Kristin Gray
Math / Kindergarten 1 2 3 4 5 / Teacher



All Grades / All Subjects / Tch Tools

Lesson Idea

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