Math lesson plan · 6th grade (Year 7 in England) · 30 minutes
Choose the best average and see how outliers affect it
Statistics and probability
CCSS 6.SP.B.5.DEngland: KS3 StatisticsEngland: GCSE Foundation Statistics
Objective and success criteria
Students will: Choose the best average and see how outliers affect it.
- 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: Calculate the mean, including decimal answers; Find the median of an even-sized data set
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 (Calculate the mean, including decimal answers; 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.
- Data (kg of recycling collected each week): 15, 15, 35, 47, 40. Find the mean. → 30.4Prompt: Add all the values.
- Find the median: 3, 31, 29, 13, 27, 32, 25, 11 → 26Prompt: Put the values in order first.
- Four runners' 100 m times in seconds: 12.9, 13.1, 12.7, 14.4. Find the mean time. → 13.275Prompt: Add the four times carefully, lining up decimal points.
Hook · 3 min
- Take a quick class survey (favorite fruit, travel to school) and ask what the results tell us.
- Share the objective: Choose the best average and see how outliers affect it. 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: Data: 16, 14, 13, 10, 18, 88. If the outlier 88 is removed, what happens to the mean?
- Step 1: With: 26.5; without: 14.2
- Step 2: It decreases.
- Answer: It decreases
- 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.
- Data: 12, 11, 19, 17, 20, 92. If the outlier 92 is removed, what happens to the mean? (It increases / It decreases / It stays the same) → It decreasesPrompt: Is the outlier much higher or much lower than the rest?
- Weekly pocket money (in dollars) in a group: 27, 22, 26, 34, 344, 28, 29. Which average best describes a typical amount? (Mean / Median) → MedianPrompt: Is there a value far from the others?
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.
- Weekly pocket money (in dollars) in a group: 28, 23, 246, 29, 21, 23, 35. Which average best describes a typical amount? (Mean / Median) → MedianPrompt: Is there a value far from the others?
- Data: 17, 21, 10, 23, 72. By how much does the mean go down when the outlier 72 is removed? Round to 1 decimal place if needed. → 10.9Prompt: Find the mean with all 5 values.
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: Calculate the mean, including decimal answers.
- 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-6.
Free lesson plan from eurekami.com/lesson-plan-builder