Grade 9: Statistics

Warm up with a few quick statistics warm-ups on the board while the class settles, so every child starts thinking about the skill.

Different data displays suit different kinds of data. This unit covers building and reading numerical displays like stem-and-leaf plots, describing their shape, centre and spread, and choosing the most suitable display for a given data set and question. Model the method clearly, thinking aloud:

• Build a stem-and-leaf plot from a real numerical data set, splitting each value into a stem and a leaf.
• Describe the resulting shape (symmetric, skewed left/right, clustered) using the display, not just the raw numbers.
• Identify any outliers in the display and discuss whether they should influence a conclusion.
• Compare several display types (bar graph, stem-and-leaf, line graph, scatterplot) side by side on the same data where possible.
• Practise justifying a display choice: what type of data is it, and what question is the display meant to answer?

Do the first few questions of the practice worksheet together, one child explaining each step. Check for understanding before releasing the class to work alone.

Students complete the practice worksheet independently while you circulate and support.

Circulate and look for these, they are the usual sticking points:

• Building a stem-and-leaf plot with leaves out of order, making the shape harder to read at a glance.
• Describing a display's shape only in vague terms ('it's kind of spread out') instead of specific features (skewed, clustered, an outlier at X).
• Choosing a display type out of habit rather than because it suits the data and the question being asked.
• Treating an outlier as automatically an error, rather than investigating whether it is a genuine, meaningful value.

Pull the class back together. Ask one child to explain statistics in their own words, pose a single check question everyone answers on a mini whiteboard, and name what you will build on next lesson.

Use the independent worksheet as the evidence. A child who can complete it accurately and explain one answer has met the objective; anyone who cannot needs the easier level and a short reteach next session.