Tens, Ones, Explain

Overview

Students build and explain two-digit numbers using number cards and number rods, extending familiar work by representing numbers beyond the 20s and reasoning about how changing one part changes the whole number. The lesson emphasises precise mathematical language, partner checking, and explaining how they know their representation is correct.

Learning intentions

• We are learning to represent two-digit numbers using tens and ones.
• We are learning to explain the value of each digit.
• We are learning to change a number by one and describe what has changed.
• We are learning to check and justify a partner’s mathematical thinking.

Success criteria

• I can build a two-digit number with tens and ones.
• I can say how many tens and ones are in my number.
• I can explain how I know my rods match the number.
• I can describe what changes when I add one or change the ones.

Curriculum links

• English — Word Recognition / Fluency: reading decodable number labels and short mathematical prompts with growing automaticity.
• English — Writing: printing numerals correctly and legibly, with attention to size, placement, spacing, and slope.
• English — Transcription Skills / Handwriting: forming numerals correctly and keeping them on the line.
• English — Writing / Spelling practices: spelling familiar oral mathematical vocabulary such as tens, ones, more, and number when appropriate.

Lesson structure (20 minutes)

1. 0–3 min · Hook and challenge. Display the number mystery opening showing 24 and 42 built with rods, and ask, “Both numbers use a 2 and a 4—how can they be different?” Students turn and talk, then share what the position of each digit tells us. Establish that a digit’s place matters: in 24, the 2 means two tens; in 42, the 4 means four tens.

2. 3–6 min · Model precise thinking. Use the tens-and-ones modelling slides to model choosing 27, building two tens and seven ones, and checking the total. Think aloud: “I know this is 27 because I have 2 groups of ten and 7 ones. The 2 is in the tens place.” Students repeat the sentence frame, “___ has ___ tens and ___ ones.” Briefly model the common error of building 7 tens and 2 ones, and ask students to explain why it is not 27.

3. 6–14 min · Partner build, check, and change. Put students into pairs and give each pair a pile of number cards and number rods. One student chooses a card and builds the number while their partner watches, checks, and asks the questions on the partner challenge slides:

• “What number did you pick?”
• “How many tens do you need?”
• “How many ones do you need?”
• “How do you know you have built the number correctly?”
• “What would you need to change to make it one more?”
• “What would happen if we changed the ones?” Students swap roles after each turn. Encourage them to choose numbers from 20–59, including several numbers in the 20s and numbers with zero or a large number of ones, such as 30, 28, and 39. Circulate and listen for confusion between tens and ones, especially with 21–29. Prompt rather than tell: “Show me the tens,” “What does the first digit tell us?” and “Can you say that as a full sentence?” If a student builds 29 as two ones and nine tens, rebuild 20 first, then add nine ones and compare.

4. 14–17 min · Record and reason. Distribute the tens-and-ones reasoning sheet. Students complete two quick representations: draw or record the rods for a number, then show what changes when one is added or when the ones digit changes. Partners read their answers aloud to one another using the sentence frame, “I changed ___, so the number became ___.” Support students to use numerals and words; accept oral explanations where writing is still developing.

5. 17–20 min · Whole-class check and conclusion. Give each student a number card and ask them to quickly build it with the rods. Choose several students to share their number and explain how many tens and ones they used. Use the plenary and exit prompt to ask, “What did we notice about numbers in the 20s?” Guide students towards: “The 2 tens stay the same while the number of ones changes.” Finish with a final comparison, such as 24 and 29, asking, “What changed? What stayed the same?”

Resources

• Number cards from 20–59, including 21–29, 30, 38, 39, and numbers with zero ones
• Number rods or base-ten equipment
• One set of rods and cards for each pair
• the complete tens-and-ones teaching deck
• the tens-and-ones reasoning sheet
• Whiteboard and marker
• Pencils and erasers

Assessment

• During partner work, check whether students match the first digit to tens and the second digit to ones, particularly for numbers in the 20s.
• Listen for explanations that use the language tens, ones, more, and change, rather than answers given without reasoning.
• Collect or quickly scan the worksheet and note whether students can represent a number, make it one more, and identify what stayed the same when only the ones changed.

Differentiation

• Support students with a tens-and-ones mat, colour-coded place positions, and the sentence frame: “___ tens and ___ ones make ___.” Model numbers using a full group of ten before adding individual ones.
• For students who confuse 21–29, repeatedly build 20 first, keep the two tens together, and add or remove only the ones while saying each change aloud.
• Extend confident students with numbers to 59, comparison questions such as “Which is greater: 28 or 38? How do you know?”, and challenges where they must change a number in two different ways to make it one more.
• Pair students thoughtfully, provide oral rehearsal before writing, and allow students with fine-motor or language needs to point, build, and explain verbally while an adult records their words.