Classroom activity Grade 8 Health & Consumer Science
Brackenfield Water-Use Trend Trackers: A Grade 8 Scatter Plot Activity
A grade 8 activity where groups scatter-plot household size against weekly water use, describe the association, and fit a line to predict a larger household's use.
Objectives
- Students will construct a scatter plot from a table of household size and weekly water use.
- Students will describe the association and informally fit a line to the data.
- Students will use their fitted line to predict the water use of a larger household.
Vocabulary
Key words: scatter plot, association, line of best fit, outlier
Teacher overview
This is a small-group data activity for pairs or trios. Each group receives the same table of ten fictional households, listing how many people live in each home and how many gallons that home used in one week. Groups plot the data, describe the pattern they see, draw a line that fits the points, and use the line to predict the weekly use of a household not in the table. The activity teaches that water use tends to rise with household size, and that a scatter plot with a fitted line lets a utility or a family estimate use for a size they have not measured directly.
Activity Directions
- Before class, print the data handout, which includes the ten-household table and a blank grid with household size on the horizontal axis and weekly water use on the vertical axis. Hand one to each group along with a ruler.
- Groups begin by plotting all ten households as points on the grid. Remind them to scale the vertical axis so the largest value fits.
- Once points are plotted, groups answer handout question 2, describing whether the association is positive or negative and whether it looks roughly linear.
- Groups answer handout question 3, checking for any point that sits far from the overall pattern.
- Using a ruler, each group draws a single straight line that comes as close as possible to the points, then answers handout questions 4 and 5 about the line's slope and a prediction.
- Groups finish with handout question 6, explaining what the slope means in everyday terms.
- End the activity when every group has drawn a line and answered all six questions.
- Debrief as a whole class: have two groups show their lines and compare slopes, then ask why two reasonable lines can still give slightly different predictions, and why a utility might still find such an estimate useful for planning.
Student Handout
The town of Brackenfield is fictional. Its water utility recorded the weekly water use of ten households one summer. Plot the data, then answer the questions.
| Household | People | Weekly water use (gallons) |
|---|---|---|
| A | 1 | 600 |
| B | 2 | 1,050 |
| C | 2 | 1,300 |
| D | 3 | 1,500 |
| E | 3 | 1,750 |
| F | 4 | 2,050 |
| G | 4 | 2,300 |
| H | 5 | 2,600 |
| I | 6 | 2,900 |
| J | 6 | 3,150 |
- Plot all ten households as points, with People on the horizontal axis and Weekly water use on the vertical axis.
- Describe the association between household size and weekly water use. Is it positive or negative, and does it look roughly linear?
- Does any single household sit far from the overall pattern? If so, name it; if not, say so.
- Draw a straight line that best fits your points. Estimate its slope in gallons per additional person.
- Use your line to predict the weekly water use of a 7-person household in Brackenfield.
- Explain what the slope of your line means for a family thinking about how their size affects their water use.
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: A scatter plot that rises from lower left to upper right, with points climbing as household size increases.
- Answer: A positive, roughly linear association: larger households tend to use more water each week, and the points rise in a fairly straight band.
- Answer: Answers will vary. Most groups will say there is no strong outlier, though a few may flag household C or J as sitting slightly above or below the band; accept any reasonable choice with justification.
- Answer: About 500 gallons per additional person; accept slopes from roughly 400 to 600 gallons per person depending on the line drawn.
- Answer: About 3,500 to 3,900 gallons; accept any prediction consistent with the group's own line extended to 7 people. A least-squares line of best fit through the ten households predicts about 3,550 gallons, so a carefully drawn line can land near the low end of that range and should be marked correct.
- Answer: The slope estimates how many more gallons a household tends to use each week for each additional person, so a family can gauge how adding a member might raise their use.
Differentiation
Support
Provide a grid with the axes already scaled and labeled, and plot the first two households as models. Let students who need it use the plotted points to answer the description questions before attempting the line of best fit.
Extension
Ask groups to compute the actual gallons-per-person for the smallest and largest households and discuss why per-person use is not perfectly constant, connecting the idea that a best-fit line summarizes a trend rather than describing every household exactly.
ELL supports
Pre-teach scatter plot, association, slope, and outlier with a simple labeled example plotted on the board. Provide sentence frames for questions 2 and 6, such as "The association is ___ because ___" and "The slope means ___ for each extra person."
Extensions
Groups can gather anonymous data from the class, such as household size and number of loads of laundry per week, plot it the same way, and describe whether that association looks as clean as the Brackenfield data. Comparing a tidy dataset to a messier real one reinforces how closely points must hug a line before a prediction can be trusted.