Mississippi Math 2.NBT.9

Math2nd GradeNumber and Operations in Base Ten (NBT) Understand Place Value

The Standard

Explain why addition and subtraction strategies work, using place value and the 3 properties of operations.

2025 Mississippi College- and Career-Readiness Standards for Mathematics · Use Place Value Understanding and Properties of Operations to Add and Subtract

Teacher's field guide

What This Standard Means

What Students Need to Do: Students break numbers into tens and ones to add or subtract. They use drawings, blocks, or equations to explain why each step works.
What Mastery Looks Like: For 46 + 27, a student can regroup the addends as 40 + 20 + 6 + 7 and explain how 13 ones become one ten and three ones. For 53 - 28, they can remove 20, then 8, and explain why that removes 28 altogether.
Common Misconceptions: Some students write 46 + 27 = 613 because they do not trade 10 ones for a ten. Others think they can switch the numbers in subtraction or subtract whichever digit is larger in each column.
How to Assess It: Exit ticket: Solve 53 - 28 by removing 20, then 8. Draw tens and ones, and explain why those steps subtract 28.

Lesson moves

Ways to Teach It

Build 52 with base-ten blocks, trade one ten for 10 ones, then remove 18 and explain why the trade did not change 52.
Write why 26 + 34 equals 34 + 26, then show how 26 + 14 + 20 gives the same total.
Play memory with equation cards 37+25, 25+37, 37+26, and 37+26+0; explain why each pair matches.
Show a supply note with 63 pencils and 28 handed out; students draw tens and ones to explain how many remain.

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