The Otter Effect
An original science article about sea otters, urchin barrens, and the kelp forests that collapsed and came back — carrying TWO central ideas at once, the way real texts do. Students find both, trace how each develops, prove they're distinct with several pieces of evidence, and write the objective summary that holds both.
Common Core standards covered
- RI.7.1Cite several pieces of textual evidence to support analysis of what the text says explicitly as well as inferences drawn from the text.
- RI.7.2Determine two or more central ideas in a text and analyze their development over the course of the text; provide an objective summary of the text.
© Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
Teacher-facing overview
Big idea: Determine two or more central ideas in a text and analyze their development over the course of the text; cite several pieces of textual evidence; provide an objective summary.
Student target: “I can determine two central ideas in one text, trace each one's development with several pieces of evidence, explain how the ideas relate without collapsing them into one, and write an objective summary that carries both.”
Success criteria: I can state both central ideas as separate, arguable claims. · I can sort evidence by which idea it serves — including evidence that serves both. · I can trace each idea's development: introduced, proven, complicated. · I can write a summary a marine biologist and a bored reader would both sign.
Essential question
Grade 6 asked for A central idea. Real texts rarely carry just one. How do you find TWO ideas braided through the same paragraphs, prove they're genuinely distinct, and hold both in one honest summary?
Learning target: I can determine two central ideas in one text, trace each one's development with several pieces of evidence, explain how the ideas relate without collapsing them into one, and write an objective summary that carries both.
Success criteria
- I can state both central ideas as separate, arguable claims.
- I can sort evidence by which idea it serves — including evidence that serves both.
- I can trace each idea's development: introduced, proven, complicated.
- I can write a summary a marine biologist and a bored reader would both sign.
Why this matters
RI.7.2's quiet upgrade from Grade 6 is one word: determine 'TWO OR MORE central ideas.' Students trained on one-idea texts either miss the second idea entirely or mash both into a mush claim ('nature is connected'). This article is built as a clean braid: idea one (a keystone species can hold up an entire ecosystem) is announced, mechanized, and proven by the fur-trade collapse; idea two (recovery is real but fragile — no single species guarantees it) arrives through the stuck population and the sea star shock; and ¶7 states both and denies the contradiction, modeling exactly the both-and reading the standard demands. The objective summary that holds two ideas without editorializing is the hardest two sentences in Grade 7 — and the most useful.
Students should already be able to
- Central idea vs. topic (Grade 6 level).
- The evidence-web habit (from Route 12, ideally).
- Citing by paragraph number.
Where this shows up outside the classroom
Assessment plan
Formative — for feedback during the lesson
- Warm-up — two-meanings examples with evidence.
- Sweep check — the hinge and shared infrastructure marked.
- Ledger circulation — distinctness tested before summaries drafted.
Summative — the graded evidence: Exit ticket (both claims + paired evidence + the no-contradiction sentence) plus the ledger and summary; the third-idea case and braid-your-own rank as extension evidence.
The passage: “The Otter Effect”
An original informational article written for this lesson (≈700 words). The ecology and history are documented; reproduce freely for your classroom.
¶1 In the kelp forests off the California coast, everything depends on an animal that spends most of its day floating on its back, cracking shellfish open with a rock. The sea otter looks like a comedy act. It is closer to a keystone — the wedge-shaped stone at the top of an arch that every other stone leans on. Pull the keystone, and the arch does not sag. It falls.
¶2 Here is the arch. Sea otters eat sea urchins — enormous quantities of them, up to a quarter of their own body weight in food every day, because otters, unusually for marine mammals, have no blubber and must burn calories constantly to stay warm. Sea urchins, left alone, eat kelp. Not nibble: mow. An unchecked urchin population can chew through a kelp forest's holdfasts and convert a hundred-foot underwater canopy into what biologists call an urchin barren — a bald seafloor carpeted in spines, where almost nothing else can live.
🔒 The full text — 7 numbered paragraphs, plus the photocopy-ready handout — ships in the kit. See plans →
The task students work on
The class hunts BOTH central ideas, states each as a claim, and runs the two-color sweep: evidence sorted by which idea it serves — with special handling for shared infrastructure (¶2's chain serves both) and the hinge (¶5 proves one idea while planting the other). Then twin development lines: introduced → proven → complicated, for each idea. The finish: a two-sentence objective summary carrying both ideas, tested by signature.
The two-ideas ledger — each idea claimed, evidenced, and traced.
| Central idea ONE | Central idea TWO | |
|---|---|---|
| Stated as a claim | ||
| Introduced at (¶) | ||
| Strongest proof (quoted, ¶) | ||
| Complicated or limited at (¶) |
Anticipated student strategies
Two-color sweeping first because the braid must be seen in the text. The mash confronted second — the distinctness test is the lesson's rigor. Turn hunting last as the transferable shortcut for every future text.
- Two-color sweeping. The student assigns each evidence-bearing sentence to idea one or idea two, discovering the shared ¶2 infrastructure and the ¶5 hinge.
The intended method — the sweep makes the braid physical. Share first.
🔒 2 more anticipated strategies with select-and-sequence guidance are in the full lesson. See plans →
Lesson script
Collect examples and push on the how-do-you-know: certain scenes only make sense for the second meaning; the ending answers a question the surface never asked. Name the lesson: Grade 7's standard says 'two or more central ideas' — today's article braids two, states both near the end, and even tells you they don't contradict. Our job is to untangle the braid without cutting it.
Listen for: Not necessarily — a braid needs both strands. The test isn't which is realer; it's whether each has its own evidence. Keep this for the ledger.
The full article is in the workbook and the handout. The sweep produces the article's shape on the board: ¶1–¶4 nearly all idea-one color; ¶5 mixed (the hinge — recovery proves idea one, 'stuck' plants idea two); ¶6 nearly all idea-two; ¶7 deliberately both. The double-colored sentences are the discussion's gold: ¶2's chain is shared infrastructure — both ideas run on otters-urchins-kelp.
- Two colors; double-coloring allowed and interesting.
- Watch ¶5 — the hinge where one idea's proof plants the other.
Listen for: Same idea, both directions: remove the keystone, arches fall; restore it, arches rebuild. Idea two hasn't arrived yet — it needs ¶6's shock. Precision about WHERE ideas live is the skill.
🔒 The remaining 4 steps — fully scripted with teacher-says lines, discourse questions, look-fors, and interventions — are in the full lesson. See plans →
Misconceptions and how to respond
- “The central idea is 'sea otters are important.'” That's idea one flattened — and it can't explain why ¶6 exists. A text's ideas must account for ALL its paragraphs; anything that leaves the sea star homeless is incomplete. Grade 7's standard says two or more for exactly this reason.
- “Two ideas means the article is confused or contradicts itself.” — the teacher response is in the full lesson.
- “The second idea is just the first idea's exception.” — the teacher response is in the full lesson.
- “A summary should pick the more important idea and lead with it.” — the teacher response is in the full lesson.
🔒 Every misconception ships with a tested classroom response. See plans →
Scaffolded practice
The workbook follows gradual release rather than a page of blank prompts: 2 fully worked, 2 partially completed, then 4 independent.
- I doLiteral first — the chain. Reconstruct the otter-urchin-kelp mechanism from ¶2–¶3 with the numbers that power it.
🔒 7 more prompts across all three release tiers are in the full lesson. See plans →
Worked solutions and scaffolds for every prompt are in the downloadable kit, included with membership. See plans and pricing.
Exit ticket
- State both central ideas — two sentences, no 'and' in either.
🔒 2 more exit-ticket questions are in the full lesson. See plans →
Worked answers, the completed answer tables, and the scoring rubric are in the downloadable kit, included with membership. See plans and pricing.
Printable handouts in the kit
All handouts are in Printable_Handouts.pdf inside the kit download.
Materials and classroom resources
Student experience
Students enter through a low-floor prompt, build or sketch a model, test a strategy, revise their thinking, collaborate, and present a final solution. The task remains accessible while allowing for sophisticated reasoning.
Detailed facilitation notes
- Step 1: First read: the article straight through, no marking. Ask: “What do you notice?”, “What could you try next?”, and “How can you prove that?”
- Step 2: Second read: two colors — evidence for idea one, evidence for idea two. Ask: “What do you notice?”, “What could you try next?”, and “How can you prove that?”
- Step 3: Trace both developments: where does each idea start, deepen, and complicate? Ask: “What do you notice?”, “What could you try next?”, and “How can you prove that?”
- Step 4: Write the objective summary that carries BOTH ideas in two sentences. Ask: “What do you notice?”, “What could you try next?”, and “How can you prove that?”
Differentiation and inclusion
Support: The two-color sweep makes the braid visible; extend with the tension question (do the ideas argue?) and the third-idea hunt.
Language support: “I started by…”, “My model shows…”, and “I know my answer is reasonable because…”.
Extension: Require a second solution, alter a condition, or have students write a challenge for another group.
Accessibility: Manipulatives, enlarged visuals, oral response choices, partner reading, and reduced-copy student pages.
Assessment plan
Formative checks: Strategy choice, accuracy, representation, collaboration, and explanation.
End evidence: Both central ideas stated as claims, two cited pieces of evidence per idea, and the two-sentence objective summary.
Mastery: The student completes the task accurately and explains the strategy with limited prompting.