Classroom activity Grade 7 Health & Consumer Science

Sampling the System: A Tanner's Bend Water-Testing Game

A grade 7 activity where student teams draw tap samples across a fictional town to learn why one sample can't judge a whole system's water quality.

Grade: Grade 7
Subject: Health & Consumer Science
Material: Classroom activity
Time: 40 min
Prep: Low prep
Materials: Prepared deck of 100 tap cards per group, Tally sheets, Paper bags or envelopes

Standards

7.SP.A.1 Common Core Math

Understand that statistics can be used to gain information about a population by examining a sample of the population; generalizations about a population from a sample are valid only if the sample is representative of that population.

How this material aligns: Teams draw random samples of tap cards and compare small and larger samples against the true share, learning that a generalization holds only when the sample is representative, as this standard names.

All materials for 7.SP.A.1 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-17.

Objectives

Students will draw random samples and estimate the share of high-lead taps in a system.
Students will compare small and larger samples against the true share.
Students will explain why a representative sample is needed to judge a whole system.

Vocabulary

Key words: sample, representative, estimate, monitoring

Teacher overview

This is a small-group sampling game for groups of four or five students. Each group receives a bag of 100 cards that stand for the 100 taps in the fictional town of Tanner's Bend; a set number of the cards are marked "high," meaning that tap tested above a contaminant level. Groups draw samples without looking, estimate the share of high taps, and compare their small and larger samples against the true share the teacher reveals at the end. The activity shows why a water utility tests many taps rather than one, since a small or lucky sample can badly misjudge the whole system.

Activity Directions

Before class, prepare one bag per group with 100 cards representing 100 taps in the fictional Tanner's Bend system. Mark exactly 12 of the cards "high" and leave the other 88 blank; shuffle each bag. Do not tell students how many are high.
Seat students in groups of four or five and give each group a bag and a tally sheet. Explain that the bag is the town's water system and each card is one tap.
Round one: each group draws 5 cards without looking, tallies how many are marked "high," records the share as a percent, and returns the cards and reshuffles.
Have each group announce its round-one estimate. Write the estimates on the board and point out how widely they differ, from groups that drew zero high cards to groups that drew one or two.
Round two: each group now draws 20 cards, tallies the "high" count, and records the share as a percent again.
Collect the round-two estimates on the board next to the round-one estimates. Ask groups to notice whether the larger samples cluster more tightly together.
Reveal the true share: 12 of 100 taps, or 12 percent, are high. Have each group compare both of its estimates to the true value.
End the game after the reveal and gather the class for the debrief questions below.

Sampling the System: A Tanner's Bend Water-Testing Game — Grade 7 Health & Consumer Science

Name: ____________________________ Date: ______________

Student Handout

Debrief questions. Answer these after the teacher reveals the true share of high taps.

Round one drew 5 cards per group. Why did the round-one estimates vary so much from group to group?
Round two drew 20 cards per group. Did the round-two estimates come closer to the true 12 percent?
Why does a real water utility test many taps across the town instead of just one?

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: With only 5 cards drawn, one lucky or unlucky high card swings the percent a lot, so small samples are unreliable for judging the whole system.
Answer: Yes, in general the 20-card samples cluster nearer the true 12 percent because a larger sample is more representative of all 100 taps.
Answer: One tap cannot represent every home, so utilities sample many locations to make sure the estimate of contamination reflects the whole system, not a single lucky spot.

Differentiation

Support

Give these groups pre-drawn samples already counted, so they focus on turning counts into percents and comparing them to the true share rather than managing the draw and tally at once.

Extension

Ask a group to combine every group's round-two sample into one large pooled sample, compute the pooled percent, and explain why the pooled estimate is usually the closest of all to the true 12 percent.

ELL supports

Pre-teach "sample," "representative," and "estimate" with a quick demonstration draw at the front of the room. Provide a tally sheet with the percent formula already printed and a sentence frame: "Our sample was ___ percent high, and the true share was ___ percent."