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Math lesson plan · 7th grade (Year 8 in England) · 30 minutes

Compare two groups using centre and spread

Statistics and probability

CCSS 7.SP.B.3CCSS 7.SP.B.4England: KS3 StatisticsEngland: GCSE Foundation Statistics

Objective and success criteria

Students will: Compare two groups using centre and spread.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Mean absolute deviation (MAD); Find quartiles and the interquartile range

Leads to: the next skill in this area.

Materials: Squared paper for charts, Class survey data, Sticky notes for a live chart, Mini whiteboards and pens, Printed student sheet (below).

Warm-up · 4 min

  • Quick retrieval from earlier learning (Mean absolute deviation (MAD); Find quartiles and the interquartile range). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. The mean of 10, 10, 10, 17, 13 is 12. Find the mean absolute deviation. → 2.4Prompt: Find how far each value is from the mean (ignore signs).
  2. Find the upper quartile (Q3) of: 10, 7, 28, 19, 35, 35, 36, 24, 4, 3, 32 → 35Prompt: Order the data and find the median.
  3. Kofi's scores: 7, 10, 13, 10. Sofia's scores: 2, 18, 10, 10. Both have mean 10. Whose scores are more consistent (smaller MAD)? (Kofi / Sofia) → KofiPrompt: MAD measures how spread out the data is around the mean.

Hook · 3 min

  • Take a quick class survey (favorite fruit, travel to school) and ask what the results tell us.
  • Share the objective: Compare two groups using centre and spread. Read the success criteria together.

I do: model it · 7 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: Class A's mean height is 145 cm and Class B's is 157 cm. Both have a mean absolute deviation of 3 cm. The difference in means is how many MADs?
  • Step 1: 157 − 145 = 12
  • Step 2: 12 ÷ 3 = 4
  • Answer: 4
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 6 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. Class A's mean height is 153 cm and Class B's is 165 cm. Both have a mean absolute deviation of 3 cm. The difference in means is how many MADs? → 4Prompt: Find the difference between the means.
  2. Minutes of daily reading. Ben's group: 20, 23, 16, 26, 23, 23, 15. Omar's group: 29, 32, 24, 34, 29, 31, 21. Using medians, which group typically reads for longer? (Ben's group / Omar's group / They are the same) → Omar's groupPrompt: Order each list and find the middle value.

You do: independent practice · 7 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 6 questions are on the student sheet below, with answers in the key.

Exit ticket · 3 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. Two basketball players' points per game: Ravi has median 18 and IQR 11; Lucia has median 18 and IQR 13. Who is more consistent? (Ravi / Lucia) → RaviPrompt: Consistency is about spread, not the average.
  2. Minutes of daily reading. Hiro's group: 30, 17, 19, 29, 15, 24, 16. Ava's group: 38, 22, 24, 38, 21, 29, 22. Using medians, which group typically reads for longer? (Hiro's group / Ava's group / They are the same) → Ava's groupPrompt: Order each list and find the middle value.

Watch out for

  • Forgetting to put data in order before finding the median.
  • Reading a bar's height wrongly when the scale goes up in 2s or 5s.

Support and stretch

Support

  • Review first: Mean absolute deviation (MAD).
  • Use concrete materials: squared paper for charts.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-7.

Free lesson plan from eurekami.com/lesson-plan-builder

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Compare two groups using centre and spread

Name

Date

Score/ 6

  1. Question 1

    Minutes of daily reading. Omar's group: 10, 17, 24, 19, 24, 13, 29. Noah's group: 14, 23, 28, 25, 30, 18, 34. Using medians, which group typically reads for longer?

    • A. Omar's group
    • B. Noah's group
    • C. They are the same

  2. Question 2

    Class A's mean height is 144 cm and Class B's is 152 cm. Both have a mean absolute deviation of 4 cm. The difference in means is how many MADs?

    Answer

  3. Question 3

    Two basketball players' points per game: Felix has median 18 and IQR 6; Isla has median 18 and IQR 3. Who is more consistent?

    • A. Felix
    • B. Isla

  4. Question 4

    Minutes of daily reading. Elena's group: 24, 12, 17, 17, 12, 10, 27. Isla's group: 27, 14, 20, 22, 14, 11, 28. Using medians, which group typically reads for longer?

    • A. Elena's group
    • B. Isla's group
    • C. They are the same

  5. Question 5

    Class A's mean height is 146 cm and Class B's is 156 cm. Both have a mean absolute deviation of 5 cm. The difference in means is how many MADs?

    Answer

  6. Question 6

    Two basketball players' points per game: Ben has median 18 and IQR 10; Liam has median 18 and IQR 12. Who is more consistent?

    • A. Ben
    • B. Liam

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Answer key: Compare two groups using centre and spread

  1. 1. B. Noah's group

  2. 2. 2

  3. 3. B. Isla

  4. 4. B. Isla's group

  5. 5. 2

  6. 6. A. Ben