NY Next Generation Math NY-2.NBT.9

Math2nd GradeUse place value understanding and properties of operations to add and subtract.

The Standard

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

New York State Next Generation Mathematics Learning Standards

Teacher's field guide

What Students Need to Do: Students explain why an addition or subtraction strategy works using place value and operation properties. They may support the explanation with objects or drawings.
What Mastery Looks Like: The student explains that breaking 47 + 36 into tens and ones preserves the total. The student connects each step to regrouping, commutativity, associativity, or the relationship between addition and subtraction.
Common Misconceptions: Students may describe steps without explaining why they preserve value. They may name a property that does not match the move or rely only on a rule.
How to Assess It: Show the strategy 58 + 27 = 50 + 20 + 8 + 7. Ask students to explain why it works using place value and a drawing.

Lesson moves

Build one calculation in two ways with base-ten blocks and connect each move to place value or an operation property.
Ask students to explain why adding tens to tens and ones to ones gives the same total.
Play strategy-proof match with worked calculations, place-value drawings, and explanations of why each method works.
Explain a mental strategy used to update a classroom count after items are added or removed.

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