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.

Since studying an entire population is often too costly or slow, statisticians study a sample instead. This unit covers the different ways a sample can be chosen, how sample size affects reliability, and why a poorly chosen sample can mislead. Model the method clearly, thinking aloud:

• Contrast a census (everyone) with a sample (a subset), discussing when each is practical.
• Introduce random, systematic and convenience sampling, with a real example of each and a discussion of who might be missed.
• Explain representativeness: a good sample reflects the population's key characteristics, not just whoever was easy to ask.
• Compare a small sample with a larger one on the same question, showing how a bigger sample usually reduces chance variation.
• Critique a real or invented survey (e.g. an online poll) for sampling bias, identifying who was excluded and why it matters.

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:

• Assuming any sample is automatically representative just because it is large.
• Confusing a convenience sample (easiest to reach) with a random sample (equal chance for everyone).
• Believing a sample must include a fixed percentage of the population to be reliable, rather than being about HOW it was chosen.
• Overlooking who a sampling method excludes (e.g. a phone survey during work hours misses people at their jobs).

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.