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Classroom activity Grade 8 English Language Arts

The Evidence Auction on Idersby's Membrane Plant

A grade 8 ELA activity: teams bid limited credits on twelve evidence cards about a fictional city's reverse osmosis plant, then build a written case from what they won.

Objectives

  1. Students will judge the value of a piece of evidence before knowing which claim they must argue.
  2. Students will build a written case using only the evidence they hold.
  3. Students will identify irrelevant, anecdotal, and popularity-based evidence in a set.

Vocabulary

Reverse osmosis
Reverse osmosis cleans water by pushing it through a membrane with holes so tiny that salt and most other dissolved things cannot fit through. It can even turn seawater into fresh water.

Also: relevance, anecdote, brackish, concentrate, wholesale rate

Teacher overview

Teams of three or four bid limited credits on twelve evidence cards about a fictional city's water decision, and only afterward learn which side they must argue. Because a team cannot know in advance which cards it will need, the bidding forces students to price evidence by how much work it could do rather than by whether they agree with it. The misconception this activity targets is the habit of treating any specific-sounding statement as strong evidence, which is why the card set includes a repainted water tower, a grandmother's recollection, and a count of how many speakers favored the plan. Reserve at least ten minutes for the debrief, and spend part of it on the cards that drew no bids, since asking a team why it passed on a card brings out the reasoning the auction is meant to teach.

Activity Directions

  1. Before class, cut apart one set of the twelve evidence cards from the Student Handout for yourself to read aloud, and give every student a full handout. The city of Idersby is fictional, and its figures belong to the scenario.
  2. Form teams of three or four. Give each team a bidding sheet and tell them they have 100 credits for the whole auction, with no credits added later.
  3. Read the situation aloud from the top of the handout. The city of Idersby has salty groundwater. It can build a reverse osmosis plant that pushes water through membranes to remove salt, or it can keep buying treated water from the Quennick district.
  4. Tell teams the two claims that will be assigned after the auction, but do not assign them yet. Claim A is that Idersby should build the plant. Claim B is that Idersby should keep buying water from Quennick.
  5. Give teams four minutes to read all twelve cards and write a private value from 0 to 30 credits beside each one.
  6. Auction the cards in order, one at a time. Read the card aloud, take open bids in increments of five credits, and stop each card at ten seconds without a new bid. Record the winning team and price. A team that runs out of credits stops bidding.
  7. After all twelve cards are sold or bidding stops, assign claims by coin flip, one claim per team. Teams do not trade cards.
  8. Give teams twelve minutes to write a case of six to eight sentences for their assigned claim, using only the cards they won. A team that holds no useful card must say so in writing and explain what it would have needed.
  9. Each team reads its case aloud. Listeners hold up one, two, or three fingers to rate how well the evidence fit the claim, and one listener explains the rating in a sentence.
  10. Close with the six debrief items at the end of the handout. Discuss items 1 through 4 as a class, and collect written responses to items 5 and 6.
The Evidence Auction on Idersby's Membrane Plant — Grade 8 English Language Arts
Name: ____________________________ Date: ______________

Student Handout

The situation. The city of Idersby is invented for this activity, and so are its numbers. Idersby draws its water from three wells. The water is brackish, meaning salty enough to taste. The city can build a reverse osmosis plant, which pushes water through membranes under pressure to strip out salt, or it can keep buying treated water from the neighboring Quennick district.

Claim A. Idersby should build the reverse osmosis plant.

Claim B. Idersby should keep buying treated water from the Quennick district.

The twelve evidence cards.

  • Card 1. Idersby's three wells test at about 1,900 mg/L of total dissolved solids, and residents describe the water as salty.
  • Card 2. A reverse osmosis plant sized for Idersby would cost about $12 million to build.
  • Card 3. Idersby pays the Quennick district about $2.4 million a year for treated water. That contract ends in six years.
  • Card 4. Reverse osmosis leaves behind a concentrated salty stream that has to go somewhere, and Idersby has no approved disposal site.
  • Card 5. The Quennick district has raised its wholesale rate three times in the last five years.
  • Card 6. A membrane plant needs a licensed operator on duty, and Idersby employs no one with that license today.
  • Card 7. The Idersby water tower was repainted in 2021.
  • Card 8. A resident writes, "My grandmother boiled the tap water her whole life and always said it never got any better."
  • Card 9. Published engineering references report that seawater reverse osmosis uses roughly 11 to 15 kWh per 1,000 gallons, against about 1 to 2 kWh for conventional treatment and delivery. Idersby's water is brackish, not seawater.
  • Card 10. The Quennick contract allows Quennick to cut deliveries to Idersby during a declared drought.
  • Card 11. A city two counties away built a brackish reverse osmosis plant in 2019 and reports that it now treats water for less than it used to pay a wholesaler.
  • Card 12. The Idersby council held four public meetings on the question, and most speakers favored building the plant.

Debrief. Answer each item in complete sentences.

  1. Which card is not relevant to either claim? Give the card number and explain what makes it irrelevant.
  2. Which card offers one person's memory instead of a record? Give the card number and explain what a record would have given the reader.
  3. Which card counts speakers rather than giving evidence about the water or the money? Give the card number and explain why counting speakers is weak support.
  4. Card 9 describes seawater plants. Name what Idersby would have to check before using Card 9 as an argument against Claim A.
  5. Which single card gives the strongest support for Claim B? Give the number and explain your choice in one sentence.
  6. Which two cards, used together, build the strongest case for Claim A? Give both numbers and explain how they work together in two sentences.

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

Answer Key
  1. Answer: Card 7. Repainting the water tower says nothing about the salt in the water, the cost of either option, or the reliability of either supply, so it cannot support or weaken either claim.
  2. Answer: Card 8. A record such as a series of dated salt measurements would show whether the water actually changed, while a remembered impression cannot be checked by anyone else.
  3. Answer: Card 12. How many speakers favored the plant measures attendance and opinion rather than cost, water quality, or supply reliability, so it does not tell the council whether the plant is the better choice.
  4. Answer: Whether the energy figure applies to brackish water at all. Brackish water carries far less salt than seawater and needs less pressure to push through a membrane, so the seawater figure may overstate what Idersby would use.
  5. Answer: Card 4. Without an approved place to send the concentrated salty stream, the plant cannot operate, which makes that card an obstacle rather than merely a cost. Accept Card 2 or Card 6 when the student argues the point clearly from the card's content.
  6. Answer: Cards 3 and 5. Card 3 establishes what Idersby now pays and that the contract expires, and Card 5 shows that the price has been climbing, so together they argue that the current arrangement is both temporary and getting more expensive. Accept Cards 3 and 10 when the student argues from supply reliability instead. Also accept a pair that includes Card 11, such as Cards 5 and 11, when the student explains how the other city's lower treatment cost and Quennick's rising rate work together.

Differentiation

Support

Assign claims before the auction for these teams so they can bid with a purpose, and give them a marked handout in which the four weakest cards are starred as "look closely." Provide a two-column chart headed "This helps my side because" and "This hurts my side because" for the writing step, and shorten the required case to four sentences.

Extension

Run a second, silent auction in which teams may buy one card from another team using credits they held back, then require each team to explain in writing why the card it bought changed the order of its reasons.

ELL supports

Preview brackish, membrane, wholesale, and concentrate with an image or quick sketch before the auction, and give a card-summary strip that restates each of the twelve cards in one short sentence. Allow teams to build their case orally with a recorder before writing, and provide the frames "Card ___ helps Claim ___ because ___" and "Card ___ does not help because it tells us about ___ instead of ___."

Extensions

Have students write the two-paragraph letter a Quennick district manager would send to the Idersby council after reading the winning case, naming which card the manager would dispute and what evidence the manager would offer instead.