Build and Check Sentences

Overview

In this first lesson of the four-lesson unit, students investigate whether addition and subtraction number sentences are true or false. They build on place-value and calculation strategies by checking both sides of an equation, using equipment, drawings, inverse operations and estimation to justify their thinking.

Learning intentions

• WALT identify whether an addition or subtraction number sentence is true or false.
• WALT calculate both sides of a number sentence accurately.
• WALT use place value, inverse operations and estimation to check an answer.
• WALT explain our mathematical thinking clearly.

Success criteria

• I can calculate both sides accurately.
• I can state whether a number sentence is true or false.
• I can explain how I know, using equipment, a drawing, a written strategy or a checking strategy.
• I can use the equals sign to mean “has the same value as”.

Curriculum links

• Mathematics and Statistics — Mathsteasers: higher-order thinking questions that challenge learners and deepen understanding.
• Mathematics and Statistics — Mathsteasers / Alignment: connecting challenge questions with relevant number knowledge and strategies.
• Mathematics and Statistics — Mathsteasers / Additional resources for advanced learners: developing mathematical reasoning and communicating thinking.
• Refreshed curriculum emphasis: learners reason, make connections, solve problems and communicate mathematical ideas.

Lesson structure (42 minutes)

1. 0–5 min · Hook: Which side is correct? Teacher displays two statements, such as 38 + 24 = 62 and 70 – 26 = 54, using the opening comparison slides, and asks, “Can both be true?” Students silently decide, show thumbs up/down, then briefly share how they checked. Do not confirm answers yet.

2. 5–13 min · Explicit teaching: Build and check. Teacher models 246 + 137 = 383 with place-value blocks or a place-value drawing, calculating each side and recording the values. Model the language: “The left side has a value of… The right side has a value of… They are the same, so the sentence is true.” Teacher then models a false sentence, using the place-value modelling slides, and demonstrates checking with the inverse operation and a sensible estimate. Students help identify the error and suggest a correction.

3. 13–18 min · Guided examples. Teacher presents three examples on the guided-check slides, including one true addition sentence, one false subtraction sentence and one sentence where estimation quickly shows the answer cannot be correct. Students calculate or estimate both sides on mini-whiteboards, hold up T or F, and explain their choice to a partner. Address the misconception that the equals sign means “the answer comes next”.

4. 18–32 min · Partner investigation. Teacher pairs students and distributes the number sentence investigation sheet and the Number Sentence Strip Cards. Students select or receive sentences, calculate both sides, decide true or false, and record evidence. They may use place-value blocks, a number line, drawings or a written strategy. Partners take turns as “solver” and “checker”; the checker asks, “How do you know?” Teacher conferences with groups, prompting students to check regrouping and explain the meaning of the equals sign.

5. 32–38 min · Reasoning share. Teacher pauses the class and displays two contrasting strategies using the partner-share and discussion slides. Invite students to compare a place-value strategy with an inverse-operation or estimation strategy. Students share one sentence they checked and complete the stem: “It is ___ because ___.” Highlight that different strategies can lead to the same conclusion.

6. 38–42 min · Plenary and exit check. Teacher displays the final prompts on the plenary slides: 425 – 178 = 247 and 199 + 206 = 405. Students independently label each true or false and write one sentence explaining one decision. Collect responses to identify who is ready for the next lesson and who needs further support with calculation or checking.

Resources

• the Build and Check Sentences slide deck
• the number sentence investigation sheet
• the Number Sentence Strip Cards
• Place-value blocks or bundled tens and ones
• Mini-whiteboards, pens and erasers
• Open number lines
• Pencils and coloured pens
• Prepared number sentences for teacher modelling

Assessment

• Listen for accurate calculation of both sides and correct use of “true” and “false” during whiteboard responses.
• During partner work, check whether students can select a suitable strategy and explain their evidence rather than guessing.
• Use the final two number sentences to group students for the next lesson: secure reasoning, calculation support, or further teaching about the equals sign.

Differentiation

• Support learners with smaller numbers, worked examples, place-value blocks, open number lines and a partner who models mathematical language. Rehearse the sentence frame: “The left side is ___. The right side is ___. They are/are not equal, so the sentence is ___.”
• Provide a reduced set of sentences for learners who need to focus on one strategy at a time. Read instructions aloud, display each step visually and allow drawing or oral explanation instead of lengthy writing.
• For EAL learners, pre-teach and repeatedly use: left side, right side, equal, value, true, false, estimate and inverse. Pair words with gestures, symbols and worked examples.
• Challenge advanced learners to create a false sentence that looks convincing, then explain the error and rewrite it so it becomes true. Ask them to compare which checking strategy is most efficient and why.