Bigger Water Share

Overview

Lesson 5 of 10 in Fraction Detectives in Action. Students compare unit fractions using water-tank models, fraction strips, measuring tapes and a floor number line, then explain why the denominator affects the size of the share. Planned for 18 students in six groups of three; add a fourth student to groups if teaching 22.

Learning intentions

• WALT compare unit fractions with denominators up to 12.
• WALT use fraction models and a number line to justify comparisons.
• WALT use <, > and = accurately.
• WALT explain why a larger denominator makes a smaller unit fraction.

Success criteria

• I can compare unit fractions such as 1/2, 1/3, 1/4, 1/8 and 1/10.
• I can use <, > and = correctly.
• I can show my thinking with a model, measuring or a number line.
• I can explain: “When one whole is split into more equal parts, each part is smaller.”

Curriculum links

• Number: recognise, represent and compare fractions as equal parts of a whole.
• Number: use mathematical symbols and explain the reasoning behind comparisons.
• Measurement: use informal and standard measurement tools to compare lengths.
• Mathematical language and communication: represent, discuss and justify mathematical ideas using materials, diagrams and symbols.

Lesson structure (60 minutes)

1. 0–7 minutes – Hook: equal water tanks

Open with the water-tank hook and learning intention slides. Show two identical rectangles: one split into two equal parts and one into eight. Ask, “Which tank share would you rather receive? How do you know?” Accept predictions, but delay confirming until students model the shares.

2. 7–15 minutes – Explicit teaching and modelling

Fold or display two identical “water tanks”. Shade one part of each to model 1/2 and 1/4. Align the parts and use a measuring tape to show that 1/2 is longer than 1/4. Record 1/2 > 1/4, stressing that the numerator remains 1: these are unit fractions. Repeat with 1/8 and 1/10. Use the comparison model and worked examples to introduce the sentence frame: “___ is greater than ___ because the whole is split into ___ parts.”

3. 15–20 minutes – Guided floor number line

Place a 0–1 floor number line across the room. Give selected students fraction cards or verbal prompts for 1/2, 1/3, 1/4, 1/8 and 1/10. Students stand where they think their fraction belongs, then check against a fraction strip. Discuss why fractions closer to 1 are larger and why 1/10 is smaller than 1/8. Refer to the floor number-line prompt for discussion questions.

4. 20–40 minutes – Group investigation: water-tank comparisons

Arrange students in groups of three: reader/card manager, model builder, and explainer; rotate roles halfway through. Give each group folded water-tank rectangles, measuring tapes, comparison cards and the fraction wall and strip cards. Students solve comparisons such as 1/2 __ 1/3, 1/4 __ 1/8, 1/8 __ 1/10 and 1/3 __ 1/3.

For each card, students build or align the shares, choose <, > or =, and prepare a brief explanation. Provide the water-tank comparison recording sheet for students to record the comparison, model or measurement, and explanation. Circulate and ask, “What stayed the same?”, “What changed?”, and “How does the denominator help you?”

5. 40–50 minutes – Explain and challenge

Each group presents one comparison, showing its model or number-line position. Other students signal agree/disagree with thumbs and give a reason. Invite advanced learners to order several fractions from greatest to least and create one misleading comparison for another group to solve. Use the share-and-explain discussion slides to maintain the explanation structure.

6. 50–57 minutes – Independent check

Students complete the final questions on the water-tank comparison recording sheet independently: compare 1/3 and 1/8, compare 1/8 and 1/10, and complete the sentence, “A larger denominator makes a unit fraction smaller because…”. Students may use a fraction strip but must choose the symbol themselves.

7. 57–60 minutes – Plenary

Return to the opening question. Ask students to complete orally: “If I share one tank among more people, each person gets a ___ share.” Revisit the WALT and success criteria using the final reflection slide. Collect the recording sheets for assessment.

Resources

• the water-tank comparison slide deck
• the water-tank comparison recording sheet
• the fraction wall and strip cards
• Identical paper rectangles or “water tanks”, folded into equal parts
• Comparison cards using unit fractions with denominators up to 12
• Floor space and masking tape for a 0–1 number line
• Measuring tapes or rulers
• Large <, > and = symbols
• Coloured pencils or counters
• High-contrast black text, uncluttered cards and colour-coded denominators

Assessment

• During group work, observe whether students partition the whole equally, compare the share sizes and select the correct symbol.
• Listen for explanations linking a larger denominator to more equal parts and therefore a smaller unit fraction.
• Use the independent check to identify students needing further work with equal partitioning, symbols or mathematical language.

Differentiation

• Support: give one comparison per card, begin with 1/2 and 1/4, provide pre-folded rectangles and allow students to align strips before recording.
• Provide sentence frames: “___ is greater than ___ because…” and “The denominator tells me…”. Pair students for reasoning and rehearse explanations before sharing.
• Use dyslexia-friendly options: high-contrast symbols, large uncluttered print, sans-serif font, colour-coded denominators, reduced copying and read-aloud instructions.
• Extension: students order five or more unit fractions, place them accurately on the floor number line, or invent a convincing misleading comparison and explain the trap.