Montana Math MT.2.OA.4

Math2nd GradeOperations and Algebraic Thinking

The Standard

Use addition to find the total number of objects arranged in rectangular arrays.

2026 Montana Mathematics Content Standards

Teacher's field guide

What Students Need to Do: Students count how many objects are in each row. They add that number once for each row to find the total.
What Mastery Looks Like: For 3 rows of 4 dots, a student writes 4 + 4 + 4 = 12. They can point to each row as they explain each 4.
Common Misconceptions: Some students write 3 + 4 = 7, adding the number of rows to the number of dots in a row. Others skip or count a dot twice as they move between rows.
How to Assess It: Draw 3 rows of 4 dots. Ask students to write an addition sentence, find the total, and circle the dots counted by each number.

Lesson moves

Give pairs 12 counters and ask them to build 3 rows of 4, then write an addition sentence for the total.
Show 2 rows of 5 dots and ask, 'Why does 5 + 5 count every dot?'
Flip array cards face down; partners turn one over, write an addition sentence, and check by counting the dots.
Show an egg carton with 2 rows of 6 spaces; ask students how many eggs fit and to show their addition.

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