Ten More, Ten Less

Overview

Students build understanding of counting by 10 (base ten) and use that knowledge to mentally find 10 more or 10 less than a two-digit number without counting. The lesson connects place-value “tens” to flexible mental strategies and explanations.

Learning intentions

Students will be able to:

• recognize that a ten is a bundle of 10 ones
• describe two-digit numbers as tens and ones
• find 10 more or 10 less than a given two-digit number by changing the number of tens
• explain their reasoning using place value words and/or drawings

Success criteria

• I can say that 10 ones make 1 ten.
• I can show a two-digit number using tens and ones (drawings or objects).
• I can find 10 more than a number like 23 by using place value (not counting by ones).
• I can find 10 less than a number like 34 by reasoning about the tens.

Curriculum links

• Number and Operations in Base Ten (CCSS.MATH.CONTENT.1.NBT.B.2a): ten is a bundle of ten ones
• Number and Operations in Base Ten (CCSS.MATH.CONTENT.1.NBT.B.2b): 11–19 is one ten and some ones
• Number and Operations in Base Ten (CCSS.MATH.CONTENT.1.NBT.B.2c): multiples of 10 represent tens and 0 ones
• Number and Operations in Base Ten: mentally find 10 more/10 less than a two-digit number and explain reasoning

Lesson structure (15 minutes total)

1. 0–3 min · Warm-up (tens). Teacher displays “10 ones” as a group and asks, “What do we call a bundle of 10 ones?” Students respond and turn-and-talk to restate in their own words.

2. 3–7 min · Mini lesson (place value picture). Teacher writes 23, shows 2 tens rods and 3 ones, and says, “23 has 2 tens and 3 ones.” Students show 23 with quick drawings or small base-ten blocks on their desk.

3. 7–10 min · Ten more move. Teacher models: “What is 10 more than 23?” Teacher points to the tens: “Add one more ten; tens go from 2 to 3, ones stay the same.” Students answer “33” and show it with rods/ones or a quick sketch.

4. 10–13 min · Ten less move. Teacher models: “What is 10 less than 34?” Teacher points to tens: “Subtract one ten; tens go from 3 to 2, ones stay the same.” Students answer “24” and show it with their materials.

5. 13–15 min · Check for understanding (exit ticket). Teacher gives one prompt: “Find 10 more than 41. Then draw a picture to show your thinking.” Students complete the answer and a simple place-value drawing.

Resources

• Base-ten blocks (tens rods and ones cubes) for each student or for pairs
• Place-value drawing template (tens boxes and ones circles) for quick sketches
• Number cards for teacher (e.g., 23, 34, 41)
• Whiteboard/markers and an easy-to-read place-value chart (Tens | Ones)
• Exit ticket slips (1 question per student)
• Timer for keeping the lesson moving at 15 minutes

Assessment

• During the warm-up, observe whether students correctly connect “10 ones” to “1 ten.”
• While modeling “10 more” and “10 less,” listen for student responses that refer to changing the number of tens (not counting by ones).
• Exit ticket: students’ correct answer for “10 more than 41” plus a place-value picture that shows the change from 4 tens to 5 tens.

Differentiation

• Support: Provide sentence frames on the board: “10 more means I ___ one ten. Ones stay ___.” and “10 less means I ___ one ten.”
• Support: For students who need it, use fewer numbers (stay in the same ones digit) and allow base-ten blocks during thinking time.
• Extension: Ask advanced students to do a second mental example: “What is 10 less than 50?” without drawing, then show how they know.
• EAL/SEN: Encourage gestures with tens rods (slide one rod on/off) and use consistent language: tens, ones, one more ten, one less ten.