Write informative/explanatory texts to examine and convey complex ideas, concepts, and information clearly and accurately through the effective selection, organization, and analysis of content.
Common Core State Standards, Grades 9-10, Writing · Read it at the source · Checked October 14, 2026
What W.9-10.2 Means in Plain English
Ninth and tenth graders explain complex ideas, like opportunity cost. They sort the material to show connections and distinctions, add headings or a table when it helps, build extended definitions with concrete examples, use the field’s precise terms, keep an objective tone and close on why it matters.
Eighth grade (W.8.2) already uses headings, definitions and quotations. Grades 9 to 10 add extended definitions, connections and distinctions between ideas, and details chosen for what the reader already knows. Grades 11 to 12 (W.11-12.2) build each element on the last into a unified whole.
W.9-10.2 I Can Statements
I can write an extended definition with a concrete example.
I can organize ideas to show connections and distinctions between them.
I can use precise terms and close on why the topic matters.
W.9-10.2 Worked Example
Both students defined the same term for readers who have never taken economics; one wrote a dictionary line, the other an explanation.
Prompt
In one section of an informative essay, explain opportunity cost to readers who have never taken economics. Write an extended definition, use one concrete example and distinguish opportunity cost from a related idea. From your notes: Anjali can work an eight-hour Saturday shift at a bike repair shop for $15 an hour or play in her chess club’s regional tournament, which charges a $20 entry fee. She already paid $35 in club dues in September.
Not YetOpportunity cost is the cost of an opportunity. For example, if Anjali goes to the chess tournament, it costs $20. Opportunity cost is very important in economics and in life.The definition repeats the term it is defining, the example names the price tag, which is exactly what opportunity cost is not, and the last sentence claims importance without showing any. A reader new to economics would finish with the wrong idea.
Meets the StandardOpportunity cost is the value of the next-best option a person gives up when making a choice. It is not the price on a ticket or a receipt; it is the cost that never appears on one. Suppose Anjali can either work an eight-hour Saturday shift at a bike repair shop for $15 an hour or play in her chess club’s regional tournament, which charges a $20 entry fee. If she plays, the $20 is only the visible part of the cost, because she also gives up the $120 she would have earned. Opportunity cost should not be confused with sunk cost: the $35 in club dues Anjali paid in September is gone whichever she chooses, so economists leave it out of the decision. Seeing the hidden cost does not tell Anjali what to choose, but it lets her weigh a $140 Saturday against what the tournament is worth to her, the same trade-off every household, business and government faces.It builds an extended definition in three steps: a precise statement, a negation that heads off the most common confusion, and a concrete case with numbers. It draws the distinction the prompt asks for, from sunk cost, uses the economist’s terms precisely, keeps an objective tone and closes on the significance of the idea rather than a slogan.
Moves to Use
Define the term in one precise sentence without reusing its own words.Say what the term is not, to head off the likeliest confusion.Ground the definition in one concrete example with real numbers.Distinguish the term from the related idea readers mix it up with.Close on why the idea matters, not on how important it is.
Common Mistakes with W.9-10.2
The circular definition
“Opportunity cost is the cost of an opportunity.”
Try this: Ban the term’s own words from its definition sentence, then have a partner who missed the lesson explain it back.
Facts in a pile
Five true sentences about costs, in the order the student found them, with no connections drawn
Try this: Have students label each pair of sentences with the relationship between them, such as contrast, cause or example, then add the transition.
The empty significance line
“In conclusion, opportunity cost is very important in economics and in life.”
Try this: Require the closing sentence to name who uses the idea and what it lets them see or decide.