Determine the main idea of an informational text and explain how its key details support it

Learning goal: This lesson teaches two parts of Ohio's 2026 standard for describing the development of an informational text, first implemented in 2027-28. You will determine the main idea of a text, identify its key details, and explain how each key detail supports the main idea.

Topic and main idea are different. The topic of a text is what it is about, often in one to three words: earthworms, beaver ponds, fire drills. The main idea is the most important point the author makes about the topic. A main idea is a whole sentence, because it says something about the topic. "Earthworms" is a topic. "Earthworms help make soil better for plants" is a main idea. So when you are asked to determine the main idea, an answer of one or two words is not finished: it names the topic and stops.

Details, key and minor. A detail is a smaller piece of information in a text: a fact, an example, a number, a description or a step. A text has many details, and they are not all equally important. A key detail helps explain or prove the main idea. A minor detail may be true and interesting, but it does not help explain the main idea. The take-it-out test is one useful check. Imagine the detail is gone. If a reader would understand the main idea less well, or would have less reason to believe it, the detail is key. If the main idea would be just as clear and just as well supported, the detail is probably minor. Then ask a second question, because two key details can support the same part of a main idea: does this detail directly show an important part of the main idea? If it does, it is key, even when another detail shows that part too. A minor detail is not a mistake; it can make a text more fun to read. It just does not hold up the main idea. A minor detail is still about the topic. A sentence about something else, such as a pet dog in an article about earthworms, is not a detail of the text at all; it does not belong.

How to determine the main idea: four steps.

1. Find the topic. Read the title, any headings and the first paragraph. Ask, "What is this whole text about?" Answer in a few words.
2. Say what each paragraph tells about the topic. Stop after each paragraph and say its point in a few words. Keep a list.
3. Look across your list. Ask, "What is the author saying about the topic that most of the paragraphs help explain?"
4. Say it in one sentence and check it. The sentence must name the topic, say something about it, and be wide enough that the key details fit under it, but not so wide that it could be about almost any text.

Stated and unstated main ideas. Sometimes an author states the main idea in one sentence, often near the beginning or at the end. Even then, do not just copy the first sentence. A first sentence is often a hook, a question or one detail meant to get you interested, so check any sentence you choose with step 4. Sometimes no single sentence states the main idea. Then you build it yourself from your paragraph list. Either way, a main idea is checked against the details; it is never guessed from the title alone.

Three ways a main idea sentence goes wrong. Too narrow: it states only one detail, such as "Earthworms eat dead leaves." That is true, but most of the other paragraphs do not fit under it. Too wide: "Animals are important." Every paragraph fits, but so would a text about horses or bees, so it tells nothing about this text. Not from the text: "Earthworms are gross." That is a reader's feeling, not the author's point, and no sentence in the text says it.

How to explain how a key detail supports the main idea. Identifying a key detail is half of the job. The other half is explaining the link, in three parts: name the detail; say which part of the main idea it helps explain; and say how, often with because or so. A sentence frame you can use: "The detail that ___ supports the main idea that ___ because it shows ___." Saying "it supports the main idea" or "it is about earthworms" is not an explanation, because it does not say what the detail shows.

How a text develops its main idea. An informational text builds its main idea one paragraph at a time. Often the first paragraph introduces the topic, each middle paragraph adds one part of the main idea with its key details, and the last paragraph sums up. Knowing this pattern helps with step 2: when a paragraph adds a new part, it probably holds a key detail.

Original article — Earthworms: Small Diggers, Big Helpers

(1) If you dig in a garden after a rain, you may find an earthworm sliding through the dirt. An earthworm has no legs, no eyes and no bones. It may not look like much, but it does important work for the soil and the plants that grow in it.

(2) Earthworms dig tunnels as they move. The tunnels let air and water move down into the soil, where plant roots can use them. Roots can also grow more easily through soil that tunnels have loosened.

(3) Earthworms eat dead leaves and bits of old plants. Some kinds of earthworms pull dead leaves down into their tunnels to eat them. The waste that comes out of an earthworm is called castings. Castings are full of nutrients, the things plants need to grow, so they add nutrients to the soil.

(4) An earthworm breathes through its skin, and its skin must stay damp for this to work. That is one reason earthworms stay underground on dry, sunny days.

(5) Gardeners are often glad to find earthworms. A garden with many earthworms usually has soil that is loose, damp and full of nutrients. In their slow, quiet way, earthworms help make soil better for plants.

A worked model inside the lesson. Step 1: the title and paragraph 1 say the topic is earthworms and the work they do for soil. Step 2, a paragraph list: (1) earthworms look simple but do important work for soil and plants; (2) their tunnels let in air and water and loosen soil for roots; (3) they eat dead leaves, and their castings add nutrients; (4) they breathe through damp skin, so they stay underground on dry days; (5) gardeners are glad to have them, because they make soil better. Step 3: paragraphs 1, 2, 3 and 5 are about how earthworms help soil and plants. Paragraph 4 is about how an earthworm breathes and where it stays. Step 4: "Earthworms make soil better for plants: their tunnels let in air and water and loosen the soil, and their castings add nutrients." Check: it names the topic, it says something about it, paragraphs 2 and 3 fit under it, and it could not be about horses. Here the author also states the main idea, in the last sentence; the check shows that sentence is the right one. The first sentence, about digging after a rain, is only a hook.

Key or minor? "The tunnels let air and water move down into the soil" is key: take it out and the reader loses one of the two ways earthworms make soil better. "An earthworm breathes through its skin" is minor: take it out and the main idea is just as clear, because it tells how a worm lives, not how it helps the soil. Explaining the link: "The detail that earthworm tunnels let air and water move down into the soil supports the main idea that earthworms make soil better for plants, because it shows how the tunnels bring roots the air and water they use."

Worked example 1 — Stated main idea: check it, do not just copy it. Original paragraph — Caring for a Library Book: "A library book belongs to everyone in town, so it needs careful handling. Keep it away from water and food. Mark your page with a bookmark instead of folding the corner. Return it on time so the next reader can borrow it." Four students offer a main idea. "Library books" names only the topic, so it is not finished. "Use a bookmark" is one detail, so it is too narrow: the water, food and return-on-time sentences do not fit under it. "Take care of things" is too wide: it could be about bikes or pets. "A library book needs careful handling because it belongs to everyone" passes the check. Here the first sentence does state the main idea, and the check proves it.

Worked example 2 — Unstated main idea: build it from a paragraph list. Original article — Winter Plans: (1) "In fall, woodchucks eat and eat until they are fat. All winter they stay in an underground burrow, where they hibernate: their bodies slow down, and they can go all winter without eating." (2) "Almost all ruby-throated hummingbirds fly south in fall, to places where flowers bloom in winter." (3) "White-tailed deer stay. They grow a thicker winter coat, and they eat twigs and buds when snow covers the grass." (4) "A woodchuck is also called a groundhog." Paragraph list: woodchucks hibernate; hummingbirds leave; deer stay and change; another name for a woodchuck. No sentence says what the paragraphs share, so build it: "Animals get through winter in different ways: some hibernate, some fly away, and some stay and change." Check: paragraphs 1 to 3 each fit under one part of it, and it is about this text.

Worked example 3 — Key or minor, and explain the support. Use Winter Plans and the main idea from worked example 2. "Deer grow a thicker winter coat": take it out, and the deer paragraph still says they eat twigs and buds, so the "stay and change" part is still shown, but with less support. The second question decides it: the coat directly shows how deer change so they can stay outside in the cold, an important part of the main idea, so it is key, and so is the twigs-and-buds detail. "A woodchuck is also called a groundhog": take it out, and the main idea is just as clear, so it is minor. It is true and interesting, but it tells nothing about getting through winter. Explanation for the key detail: "The detail that deer grow a thicker winter coat supports the main idea that animals get through winter in different ways, because it shows the third way, staying and changing, so deer can live outside in the cold." Weak explanation, for contrast: "It supports the main idea because it is about deer." That names the detail and stops; it never says what the detail shows.

Paragraph map (record task): Read the article below twice. Make a table with three columns: Paragraph, What it tells (a few words), Key or minor. Fill in one row for each of the six paragraphs. A paragraph's role depends on the main idea, so decide the main idea first: for example, paragraph 6 is key if your main idea includes the other animals that use the pond, and minor if it does not. Under the table, write the main idea in one sentence, say whether the article states it or you built it, and show your step 4 check in one line. Mark one minor detail and write the take-it-out test for it.

Independent performance: Choose an informational text of four to eight paragraphs that your teacher approves: a chapter section from a library book, a children's magazine article or a page of a science book. Success criteria: (1) you name the topic in a few words; (2) you list each paragraph's point; (3) you write the main idea as one sentence that names the topic and says something about it, and you say whether it is stated or built; (4) you show that it is not too narrow, not too wide and not your own feeling; (5) you identify two key details and give the take-it-out test for each; (6) you identify one minor detail and say why it is minor; (7) for each key detail, you explain how it supports the main idea with all three parts: the detail, the part of the main idea, and how.

Original article — The Busy Builders of the Pond

(1) A stream runs through the woods. One spring, a pair of beavers arrives. By fall, part of the stream has become a pond. How did that happen?

(2) The beavers built a dam across the stream. They cut down small trees and branches with their large front teeth. They piled the sticks across the water and packed them with mud and stones. The dam holds the water back, and a pond forms behind it.

(3) In the pond, the beavers build a home called a lodge out of sticks and mud. The lodge has entrances under the water. Because the pond is deep, the beavers can swim in and out without coming onto land, where predators such as coyotes could catch them.

(4) In the fall, beavers push branches into the mud at the bottom of the pond, near the lodge. When ice covers the pond in winter, the beavers swim out under the ice and eat the bark of the stored branches.

(5) A beaver's front teeth never stop growing. Chewing wood keeps them from growing too long. The front of each tooth is orange.

(6) Other animals use the pond, too. Ducks nest along its edges, frogs lay eggs in its quiet water, and fish swim in its deeper pools.