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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 11, 5, 5, 14, 10 is 9. Find the mean absolute deviation. → 3.2Prompt: Find how far each value is from the mean (ignore signs).
  2. Find the upper quartile (Q3) of: 22, 9, 27, 6, 39, 29, 37, 12, 50, 17, 39 → 39Prompt: Order the data and find the median.
  3. Diego's scores: 28, 30, 32, 30. Maya's scores: 24, 36, 30, 30. Both have mean 30. Whose scores are more consistent (smaller MAD)? (Diego / Maya) → DiegoPrompt: 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 157 cm and Class B's is 173 cm. Both have a mean absolute deviation of 4 cm. The difference in means is how many MADs? → 4Prompt: Find the difference between the means.
  2. Minutes of daily reading. Ines's group: 23, 10, 15, 22, 26, 24, 24. Leo's group: 31, 18, 23, 31, 33, 31, 33. Using medians, which group typically reads for longer? (Ines's group / Leo's group / They are the same) → Leo'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. Class A's mean height is 143 cm and Class B's is 147 cm. Both have a mean absolute deviation of 2 cm. The difference in means is how many MADs? → 2Prompt: Find the difference between the means.
  2. Two basketball players' points per game: Priya has median 18 and IQR 8; Zara has median 18 and IQR 11. Who is more consistent? (Priya / Zara) → PriyaPrompt: Consistency is about spread, not the average.

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. Hiro's group: 13, 25, 23, 14, 20, 20, 11. Kwame's group: 25, 33, 35, 26, 29, 31, 21. Using medians, which group typically reads for longer?

    • A. Hiro's group
    • B. Kwame's group
    • C. They are the same

  2. Question 2

    Class A's mean height is 151 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?

    Answer

  3. Question 3

    Two basketball players' points per game: Ava has median 18 and IQR 11; Zoe has median 18 and IQR 14. Who is more consistent?

    • A. Ava
    • B. Zoe

  4. Question 4

    Minutes of daily reading. Felix's group: 14, 25, 11, 17, 20, 16, 23. Elena's group: 22, 36, 23, 27, 28, 26, 35. Using medians, which group typically reads for longer?

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

  5. Question 5

    Class A's mean height is 158 cm and Class B's is 170 cm. Both have a mean absolute deviation of 4 cm. The difference in means is how many MADs?

    Answer

  6. Question 6

    Two basketball players' points per game: Amara has median 18 and IQR 6; Nia has median 18 and IQR 8. Who is more consistent?

    • A. Amara
    • B. Nia

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Answer key: Compare two groups using centre and spread

  1. 1. B. Kwame's group

  2. 2. 2

  3. 3. A. Ava

  4. 4. B. Elena's group

  5. 5. 3

  6. 6. A. Amara

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