Classroom activity Grade 6 Engineering & Design
Cobble Hill Trade-off Draft: A Water Main Upgrade Game
A card-drafting game where teams build a 3-card water main upgrade package within a point budget and test it against a town council's three design criteria.
Objectives
- Students will select a 3-card upgrade package that stays within a fixed point budget.
- Students will calculate their package's total cost and its total durability, capacity, and disruption-reduction scores.
- Students will explain why a fixed budget can prevent a design from meeting every stated design goal at once.
Vocabulary
Key words: trade-off, criteria, constraint, durability
Teacher overview
Cobble Hill's town council (a fictional town used for this game) has hired student engineering teams to propose an upgrade package for an aging water main. Teams of 3 or 4 draft from a set of 8 upgrade cards, each with a point cost and three ratings, durability, capacity, and disruption-reduction, and must choose exactly 3 cards that fit a 10-point budget. The card-drafting format resembles real infrastructure planning: every upgrade option costs points from a fixed budget, and no team can choose every high-scoring card at once, which is the kind of constrained decision a public works budget forces in practice.
Activity Directions
- Divide the class into teams of 3 or 4. Give each team its own identical set of 8 upgrade cards and 1 scorecard. Explain that Cobble Hill's town council has hired their team to design a water main upgrade package.
- Explain the cards: each card lists a point cost and three ratings, durability, capacity, and disruption-reduction, each from 0 to 3. Every team has a 10-point budget and must end the game with exactly 3 cards, keeping the total cost at or under 10 points.
- Round 1, draft blind (8 min): Before knowing the council's specific requirements, each team privately chooses its first 3-card package, aiming for a strong overall combination. Teams record their chosen cards and total cost, durability, capacity, and disruption-reduction scores on the scorecard.
- Reveal the council's criteria (2 min): Announce Cobble Hill Council's stated requirements: a durability total of at least 5, a capacity total of at least 4, and a disruption-reduction total of at least 3. Teams check their Round 1 package against all three requirements.
- Round 2, one swap (10 min): Each team may remove exactly one card from its package and replace it with one different card from its own set, keeping the total cost at or under 10 points, to try to meet more of the three council requirements.
- Round 3, final proposal (10 min): Teams finalize their 3-card package, recompute their total cost and all three totals, and prepare a short pitch stating which of the three requirements their package meets and which, if any, it does not, and why they prioritized the requirements they did.
- Each team delivers its pitch to the class. The activity ends once every team has presented, at which point the teacher reveals whether any team's package met all three requirements.
- Debrief as a whole class using the numbered questions in the Student Handout below.
Student Handout
Upgrade card set (identical set given to every team):
| Card | Point cost | Durability | Capacity | Disruption-reduction |
|---|---|---|---|---|
| A: Ductile iron pipe | 4 | 3 | 1 | 0 |
| B: Trenchless boring method | 3 | 0 | 0 | 3 |
| C: Extra-wide pipe | 3 | 0 | 3 | 0 |
| D: Extended warranty inspection | 2 | 2 | 0 | 0 |
| E: Night-shift construction crew | 2 | 0 | 0 | 2 |
| F: Basic PVC pipe | 1 | 1 | 1 | 0 |
| G: Leak sensors | 2 | 1 | 0 | 1 |
| H: Community notice plan | 1 | 0 | 0 | 1 |
Council requirements, revealed after Round 1: durability total at least 5, capacity total at least 4, disruption-reduction total at least 3. Budget: 10 points total for exactly 3 cards.
Debrief and verification questions. Answer all six using the card table above.
- Did any team's 3-card package meet all three council requirements at once? Why or why not?
- What is the best 2-of-3 combination you found, and which requirement did it leave out?
- For the card C, F, B package (extra-wide pipe at 3 points, basic PVC pipe at 1 point, and trenchless boring at 3 points), what is the package's total point cost?
- For that same card C, F, B package, what is the total durability score (card C 0, card F 1, card B 0)?
- For that same card C, F, B package, what is the total capacity score (card C 3, card F 1, card B 0)?
- For that same card C, F, B package, what is the total disruption-reduction score (card C 0, card F 0, card B 3)?
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: No 3-card combination from this deck can meet all three requirements at once.
Debrief question: "Did any team's 3-card package meet all three council requirements at once? Why or why not?" Capacity points come only from cards A, C, and F (1, 3, and 1 point each); reaching a capacity total of at least 4 always requires card C paired with either card A or card F, which uses two of a team's three card slots. Whichever pairing a team chooses, the one remaining card slot cannot supply enough durability and disruption-reduction at the same time to close both remaining gaps, since card G, the only card that raises both, adds just 1 durability and 1 disruption-reduction, far short of the gap. - Answer: Several 3-card combinations reach two of the three requirements, but none reaches all three.
Debrief question: "What is the best 2-of-3 combination you found, and which requirement did it leave out?" Card A (ductile iron pipe) plus card B (trenchless boring) plus card D (extended warranty) costs 4 + 3 + 2 = 9 points and scores durability 5, capacity 1, disruption-reduction 3, meeting the durability and disruption-reduction requirements while falling short on capacity. Card A plus card C (extra-wide pipe) plus card D costs 4 + 3 + 2 = 9 points and scores durability 5, capacity 4, disruption-reduction 0, meeting durability and capacity while falling short on disruption-reduction. A team that reached either of these packages, or a comparable one, found the best available trade-off with this deck. - Answer: 7 points.
Verification question, total cost of the card C, F, B package (extra-wide pipe, basic PVC pipe, and trenchless boring): cost 7 points (3 + 1 + 3), within the 10-point budget. - Answer: 1 durability point.
Verification question, durability total of the same package: durability 1 (0 + 1 + 0), which falls short of the durability requirement. - Answer: 4 capacity points.
Verification question, capacity total of the same package: capacity 4 (3 + 1 + 0), which meets the capacity requirement. - Answer: 3 disruption-reduction points.
Verification question, disruption-reduction total of the same package: disruption-reduction 3 (0 + 0 + 3), which meets the disruption-reduction requirement.
Differentiation
Support
Give struggling teams a partially completed scorecard with the point-cost column already totaled for a few sample 3-card combinations, so they can focus on comparing durability, capacity, and disruption-reduction totals rather than recomputing every cost sum from scratch.
Extension
Challenge teams that finish Round 3 early to find every 3-card combination that reaches a capacity total of at least 4, and explain why card C must appear in every one of those combinations.
ELL supports
Pre-teach "durability," "capacity," and "disruption" using one labeled icon per rating on the printed cards (a shield for durability, a pipe-width symbol for capacity, a construction-barrier symbol for disruption-reduction). Allow teams to present their Round 3 pitch using their completed scorecard and short phrases rather than full sentences.
Extensions
Have teams redesign one card from the set, keeping its point cost the same but changing its three ratings, and explain in writing how their new card would change the best possible 2-of-3 combination.