Montana Math MT.1.OA.7

Math1st GradeOperations and Algebraic Thinking

The Standard

Use multiple strategies to add and subtract within 20.

2026 Montana Mathematics Content Standards

Teacher's field guide

What Students Need to Do: Students add and subtract within 20. They use different methods, such as counting on, making ten, and using known doubles, and show how each method works.
What Mastery Looks Like: A student can solve 8 + 7 by making ten or using 7 + 7 + 1. They can solve 14 - 6 by subtracting 4 and then 2, and explain their steps.
Common Misconceptions: Some students count the starting number as the first step, so they get 10 for 8 + 3. Others subtract 4 from 14 to reach 10 but forget to subtract the remaining 2.
How to Assess It: Exit ticket: Solve 8 + 7 and 14 - 6. Show two different ways to solve each problem with numbers or drawings.

Lesson moves

Give pairs counters and two ten-frames; have them solve 8 + 7 by making ten, then by counting on.
Ask, “How could you solve 13 - 5 without counting back five times?” Have partners draw and explain their steps.
Write 12 addition and subtraction problems within 20 on cards; partners draw a card, solve it two ways, and check each other's work.
Post a classroom library sign: 16 books, 9 checked out. Students sketch the shelf and find books left by subtracting and counting up.

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