The main idea is what a paragraph or text is mostly about: the big point the writer wants you to understand. Supporting details are the facts, examples and reasons that prove or explain that point. A good way to find the main idea is to ask two questions. First, who or what is this about (the topic)? Second, what is the writer saying about that topic? Put those together in one sentence and you have the main idea.
The Common Core reading standard RI.4.2 asks fourth graders to determine the main idea of a text, explain how key details support it and summarize the text. Sometimes the main idea is stated in a topic sentence, often the first or last sentence. Other times it is implied, and you have to add up the clues yourself. Every passage below was written for this page. Read it carefully, answer, then check the explanation to see how the details point to the big idea.
Choose an option or type your answer, then press Check. Capital letters and extra spaces do not matter in typed answers, and units are optional.
Answer: C) Honeybees in a hive share the work, each with a job.
Every detail describes a different job, and the first sentence says bees work as a team. Gathering nectar and cleaning are details, and stinging is not mentioned.
Answer: library (also accepted: the library, town library, our town library, the town library)
The topic is who or what the passage is about: the library. The main idea is what the writer says about it, that it offers much more than books.
Answer: A) Kangaroo rats stay in cool burrows during the day.
The main idea is how desert animals beat the heat. Only the kangaroo rat sentence shows an animal staying cool.
Answer: topic sentence (also accepted: a topic sentence, the topic sentence)
A topic sentence states the main idea. The other sentences in the paragraph support it.
Answer: D) How Maple Syrup Is Made
A good title matches the main idea. Every sentence is a step in making maple syrup.
Answer: supporting detail (also accepted: a supporting detail, detail, a detail)
It is one step in the process, so it is a supporting detail. The main idea is how maple syrup is made.
Answer: D) Riding a bike is good for you, the planet and your wallet.
The other choices are each one detail. The main idea sums up all three benefits.
Answer: summary (also accepted: a summary)
A summary gives the main idea and key details briefly, in your own words, without opinions.
Answer: C) Sea otters sometimes hold paws while they sleep.
Holding paws is an interesting fact, but it does not explain how otters handle cold water. The other three do.
Answer: penguins (also accepted: penguin)
The passage is about penguins. Its main idea is that penguins are built for swimming.
Answer: D) Jada is getting ready for an important game.
The writer never says it, but every detail (early alarm, packed gear, energy breakfast) points to Jada preparing for a game.
Answer: soccer (also accepted: a soccer game, soccer game, soccer practice, a soccer match)
Cleats and shin guards are the clues. Shin guards are worn mainly in soccer.
Answer: B) In the first or last sentence
Writers often state the main idea at the start or sum it up at the end. Always check that it covers all the details.
A single interesting fact is usually a supporting detail. The main idea should cover all of the details, not just one.
If a passage is about desert animals keeping cool, “Animals live everywhere” is too big. The main idea should match what the paragraph actually covers.
The topic is one or two words (penguins). The main idea is a full sentence about the topic (Penguins are built for swimming).
A main idea or summary uses only what the writer said. Leave out your own opinions and extra facts.
Turn main idea into a printable, differentiated worksheet with an answer key, matched to grade 4.
Make a worksheet →Build a test or quiz on this topic that students answer online and that marks itself, with a class summary for you.
Build a self-marking test →Step-by-step help, quizzes and test-style practice in a safe, parent-managed student portal.
Open the student portal →No. It is often the first sentence, sometimes the last, and sometimes it is not stated at all. When it is implied, look at what all the details have in common.
The main idea is one sentence about the big point. A summary is a short retelling of the most important ideas, usually the main idea plus the key details, in your own words.