Math lesson plan · 6th grade (Year 7 in England) · 60 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 · 6 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: 18, 19, 14, 15, 22, 18, 5, 18 → 18Prompt: Put the values in order first.
- Ten students recorded text messages sent in a day: 6, 36, 59, 37, 45, 27, 46, 31, 29, 21. What is the median? → 33.5Prompt: Order the 10 values.
- Find the median: 2, 17, 32, 8, 16, 10 → 13Prompt: Put the values in order first.
Hook · 6 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 · 12 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 · 12 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 upper quartile (Q3) of: 3, 30, 30, 37, 27, 32, 1 → 32Prompt: Order the data and find the median.
- Find the interquartile range (IQR) of: 19, 46, 50, 59, 10, 31, 22, 30, 17, 38 → 27Prompt: Order the data. Split it into a lower half and an upper half.
You do: independent practice · 17 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 · 7 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 19, Q1 26, median 30, Q3 33, maximum 40. What is the range? → 21Prompt: The box goes from Q1 to Q3; the whiskers go to the minimum and maximum.
- Find the lower quartile (Q1) of: 19, 25, 46, 11, 15, 29, 30, 34, 26, 10, 49 → 15Prompt: 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