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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 16, 16, 15, 29 is 19. Find the mean absolute deviation. → 5Prompt: Find how far each value is from the mean (ignore signs).
  2. Find the lower quartile (Q1) of: 29, 24, 13, 9, 4, 7, 44 → 7Prompt: Order the data and find the median.
  3. Mei's scores: 19, 21, 23, 21. Yuki's scores: 15, 27, 21, 21. Both have mean 21. Whose scores are more consistent (smaller MAD)? (Mei / Yuki) → MeiPrompt: 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 150 cm and Class B's is 156 cm. Both have a mean absolute deviation of 2 cm. The difference in means is how many MADs? → 3Prompt: Find the difference between the means.
  2. Minutes of daily reading. Mateo's group: 29, 14, 11, 23, 20, 28, 27. Lucia's group: 32, 17, 14, 27, 22, 29, 30. Using medians, which group typically reads for longer? (Mateo's group / Lucia's group / They are the same) → Lucia'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: Ben has median 18 and IQR 12; Mei has median 18 and IQR 9. Who is more consistent? (Ben / Mei) → MeiPrompt: Consistency is about spread, not the average.
  2. Class A's mean height is 156 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? → 3Prompt: Find the difference between the means.

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. Noah's group: 25, 20, 27, 20, 11, 23, 16. Jamal's group: 31, 24, 31, 23, 14, 30, 21. Using medians, which group typically reads for longer?

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

  2. Question 2

    Class A's mean height is 148 cm and Class B's is 164 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: Maya has median 18 and IQR 8; Kofi has median 18 and IQR 13. Who is more consistent?

    • A. Maya
    • B. Kofi

  4. Question 4

    Minutes of daily reading. Maya's group: 24, 28, 16, 23, 25, 28, 23. Omar's group: 26, 34, 22, 26, 29, 30, 29. Using medians, which group typically reads for longer?

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

  5. Question 5

    Class A's mean height is 151 cm and Class B's is 160 cm. Both have a mean absolute deviation of 3 cm. The difference in means is how many MADs?

    Answer

  6. Question 6

    Two basketball players' points per game: Sam has median 18 and IQR 5; Ava has median 18 and IQR 3. Who is more consistent?

    • A. Sam
    • B. Ava

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Answer key: Compare two groups using centre and spread

  1. 1. B. Jamal's group

  2. 2. 4

  3. 3. A. Maya

  4. 4. B. Omar's group

  5. 5. 3

  6. 6. B. Ava