Maryland Math 1.NOS.E.10.a

Math1st GradeNumber and Operation Sense

The Standard

1.NOS.E.10: Add within 100 including adding a two-digit number and a one-digit number and adding a two-digit number and a multiple of 10. Understand that when adding two-digit numbers, tens are added to tens, ones are added to ones, and sometimes it is necessary to compose or decompose a ten.

Use concrete models and drawings to add.

Maryland College and Career Ready Standards for Mathematics (2025) · USE PLACE VALUE UNDERSTANDING AND PROPERTIES TO ADD AND SUBTRACT.

Teacher's field guide

What Students Need to Do: Students build each number with cubes or base-ten blocks, then draw what they built. They put the groups together and use the drawing to find the sum.
What Mastery Looks Like: A student can build and draw 26 + 17, then trade ten ones for one ten. They find 43 and explain where the new ten came from.
Common Misconceptions: Some students draw one mark for a ten and count it as one. Others count the same ones twice or forget to trade ten ones for one ten.
How to Assess It: Give students base-ten blocks and this exit ticket: Build 26 + 17, draw the blocks, and write the sum. Circle any ten made from ones.

Lesson moves

Have students build 24 + 13 with base-ten blocks, push the groups together, and sketch the result.
Show a drawing of 26 + 17 and ask, "Where did the fourth ten come from?"
Partners draw two cards labeled 11, 12, 23, or 34, add them with tens-and-ones sketches, and check each other's work.
Ask how many books are on two shelves holding 24 and 13 books; students sketch tens and ones to find the total.

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