Math lesson plan · 6th grade (Year 7 in England) · 45 minutes
Find quartiles and the interquartile range
Statistics and probability
CCSS 6.SP.B.5.CEngland: KS3 StatisticsEngland: GCSE Foundation Statistics
Objective and success criteria
Students will: Find quartiles and the interquartile range.
- 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: Find the median of an even-sized data set
Leads to: Compare two groups using centre and spread
Materials: Squared paper for charts, Class survey data, Sticky notes for a live chart, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Find the median of an even-sized data set). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Find the median: 27, 7, 39, 18, 8, 32 → 22.5Prompt: Put the values in order first.
- Ten students recorded text messages sent in a day: 15, 59, 39, 49, 29, 13, 53, 37, 23, 51. What is the median? → 38Prompt: Order the 10 values.
- Find the median: 24, 16, 10, 18, 7, 13 → 14.5Prompt: Put the values in order first.
Hook · 5 min
- Take a quick class survey (favorite fruit, travel to school) and ask what the results tell us.
- Share the objective: Find quartiles and the interquartile range. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: Find the lower quartile (Q1) of: 20, 48, 33, 36, 8, 14, 32, 2, 45, 2, 39
- Step 1: 2, 2, 8, 14, 20, 32, 33, 36, 39, 45, 48
- Step 2: Median = 32
- Step 3: Q1 = 8
- Answer: 8
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- Find the lower quartile (Q1) of: 4, 36, 12, 31, 26, 11, 30, 1, 8, 2, 40 → 4Prompt: Order the data and find the median.
- Find the interquartile range (IQR) of: 34, 32, 19, 52, 14, 60, 15, 23, 49 → 33.5Prompt: Order the data. Split it into a lower half and an upper half.
You do: independent practice · 10 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 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- A box plot of reaction times (hundredths of a second) shows: minimum 17, Q1 26, median 33, Q3 40, maximum 46. What is the interquartile range? → 14Prompt: The box goes from Q1 to Q3; the whiskers go to the minimum and maximum.
- Find the lower quartile (Q1) of: 32, 37, 2, 26, 20, 44, 3, 31, 3, 47, 10 → 3Prompt: Order the data and find the median.
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: Find the median of an even-sized data set.
- 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
- Move on to: Compare two groups using centre and spread.
- 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-6.
Free lesson plan from eurekami.com/lesson-plan-builder