Classroom activity Grade 7 Engineering & Design
Chalkmere Utility Design Review: Four Constraint Stations
A grade 7 station rotation where teams make one decision at each of four water-utility desks, then compare the constraints that pushed each role toward a choice.
Objectives
- Students will choose among competing options at each station using the station's stated constraint.
- Students will compute unit rates and percents to compare options rather than choosing by impression.
- Students will explain how two water-utility roles can reach different conclusions from the same data.
Vocabulary
Key words: constraint, unit rate, capital budget, sampling point
Teacher overview
This is a four-station rotation for teams of three or four students, run in one class period. Each station is a desk at the fictional Chalkmere water utility, and each desk belongs to a different role: the plant operator, the laboratory technician, the rate analyst, and the distribution crew leader. Every station hands the team a number to compute and a limit to test that number against, so each desk asks the same kind of decision in a different form. The rotation teaches that a water system is run by people whose constraints differ, so the same project can look sensible at one desk and unaffordable at the next.
Activity Directions
Before class (prep): Print the four station cards from the student handout and post one at each of four spread-out desks or table clusters. Print one handout per student. Place a calculator at each station. The scenario is fictional throughout, and no station requires any outside information.
Setup and framing (8 min): Group students into teams of three or four and assign each team a starting station, spreading teams evenly across the four. Explain that every station names one role at the utility, gives that role's numbers, and states the limit that role works under. Tell teams they will answer the handout questions for their current station only, then rotate on your signal.
Rotation rounds (10 min each, 40 min total): Teams work the handout questions tied to their current station, then rotate clockwise when you call time. Station 1 is the operator's desk and covers handout questions 1 and 2. Station 2 is the laboratory technician's desk and covers questions 3 and 4. Station 3 is the rate analyst's desk and covers questions 5 and 6. Station 4 is the distribution crew leader's desk and covers questions 7 and 8. The rotation ends when every team has visited all four stations, which takes exactly four rounds.
During the rounds: Circulate and ask one probing question per team per round. Useful prompts are "which number in this station is the limit, and which is the goal," and "what would you have chosen if that limit were gone." Teams that finish a station early should write a one-sentence reason for their choice before rotating.
Debrief (12 min): Bring the class back together and take answers to handout questions 1 through 8 in order, asking a different team to report each one. Then put the closing question to the whole class: the rate analyst at Station 3 has spent nearly the entire budget on two projects, so which of the other three roles would object, and on what grounds. Have every student write their answer as handout question 9 before the period ends. Close by noting that these four roles reach their desks by different routes, including a high school diploma with on-the-job training and a state operator license, a certificate or associate program in laboratory or field work, and a four-year engineering degree.
Student Handout
Suppose you are visiting four desks at the fictional Chalkmere water utility. Answer the questions for the station you are at now.
Station 1, the plant operator's desk. Chalkmere uses 72,000 gallons of water on an average day. The plant's finished-water pump moves 250 gallons per minute. The operator's limit is that the pump may run only during one shift.
How many minutes must the pump run to deliver 72,000 gallons?
How many hours is that? Round to the nearest tenth.
Station 2, the laboratory technician's desk. The distribution system has 40 sampling points. The laboratory's budget pays for 12 samples each month. The technician's limit is that budget.
What percent of the sampling points can be tested in one month?
If no point is ever repeated, how many whole months would it take to sample all 40 points once? Round up to a whole month.
Station 3, the rate analyst's desk. The capital budget for this year is $150,000. Four projects are on the list: valve replacement at $60,000, meter upgrades at $45,000, hydrant painting at $30,000, and pipe lining at $85,000. The analyst's limit is that the total may not go over the budget.
Which two projects together come closest to the budget without going over it, and what do those two cost in all?
How much of the budget is left after that pair is funded?
Station 4, the distribution crew leader's desk. Three street segments have had breaks in the last five years. Maple Row is 1,400 feet long and had 6 breaks. Kiln Street is 900 feet long and had 9 breaks. Ferry Lane is 2,100 feet long and had 7 breaks. The crew leader's limit is that only one street can be relined this year.
What is Kiln Street's break rate, in breaks per 1,000 feet?
Which of the three streets has the highest break rate per 1,000 feet?
The rate analyst at Station 3 funded two projects and spent nearly the whole budget. Name one other role at Chalkmere that would object to that pair of choices, and explain in one or two sentences what that role would say.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
These items key the nine numbered questions on the student handout, in order. The numbered steps under Activity Directions are teacher instructions and are not keyed.
Answer: 288 minutes.
72,000 gallons divided by 250 gallons per minute = 288 minutes of pump run time.Answer: 4.8 hours.
288 minutes divided by 60 minutes per hour = 4.8 hours, which fits inside a single shift.Answer: 30 percent.
12 samples divided by 40 sampling points = 0.30, which is 30 percent of the points each month.Answer: 4 months.
40 points divided by 12 samples per month = 3.33 months, which rounds up to 4 whole months because the last four points still need a month of their own.Answer: 145,000 dollars.
Pipe lining at $85,000 plus valve replacement at $60,000 = $145,000, the largest pair that stays at or under the $150,000 budget. Every other pair costs less: $85,000 with $45,000 is $130,000, and $60,000 with $45,000 is $105,000.Answer: 5,000 dollars.
$150,000 minus $145,000 = $5,000 left in the budget, which is not enough for any remaining project on the list.Answer: 10 breaks per 1,000 feet.
Kiln Street is 900 feet, which is 0.9 of a thousand feet. 9 breaks divided by 0.9 = 10 breaks per 1,000 feet.Answer: Kiln Street.
Maple Row is 6 breaks divided by 1.4, or about 4.3 breaks per 1,000 feet. Ferry Lane is 7 breaks divided by 2.1, or about 3.3. Kiln Street's 10 breaks per 1,000 feet is the highest, even though Ferry Lane is the longest street and Maple Row is not far behind in raw break count.Answer: One role with a stated objection.
Accept any of the three other roles with a reason drawn from that station's numbers. The crew leader would object that no money is left to reline Kiln Street, which has the worst break rate. The laboratory technician would object that a larger sampling budget would let the utility cover more than 30 percent of its points in a month. The operator would object that nothing in the pair improves pumping, so the plant still runs the same long shift. Strong answers name the number the objecting role would point to.
Differentiation
Support
Give these teams a handout with the division already set up for questions 1 and 3, and a printed unit-rate reminder reading "breaks divided by thousands of feet" at Station 4. Let them work Station 3 with the four project costs written on separate cards they can physically pair and total. Assign a fixed recorder role so the writing load does not fall on one student by default.
Extension
Ask these teams to write a fifth station of their own for a role not in the rotation, such as a customer service supervisor or a source water planner, including that role's numbers, its limit, and two questions with answers. Have them trade stations with another team and check whether the questions can actually be answered from the numbers given.
ELL supports
Post each station card with a simple icon showing the role at work, and pre-teach limit, budget, sampling point, and break with a labeled picture at the front of the room. Provide the sentence frame "The limit at this station is ___, so we chose ___" for the rotation, and the frame "The ___ would object because ___" for question 9. Allow teams to answer question 8 by pointing to the street name on the card.
Extensions
Have the class build one wall chart with four columns, one per role, listing every limit that appeared in the rotation. Ask students to circle any two limits that pull in opposite directions and to write a short paragraph on how a utility settles a disagreement between two of its own departments. Teams can then repeat the Station 3 decision with the constraint loosened by a quarter and report which project list they would fund instead.