Ask the students to read the title of the essay, if there is one. The title will frequently indicate the topic. In general terms, the topic describes what the essay is about. "My Life with Whales" is a title that clearly states the essay will be about the author and whales. Discuss with the students whether they can tell what the main idea is from this title. Have them suggest possible main ideas; in this case, it might be about difficult times the author suffered trying to prevent whaling boats from killing whales, ways to help beached whales get back to sea or a plea to save whale species faced with extinction. By having them read the essay quickly, they should be able to determine the topic. If every paragraph is about whales, they can justly conclude the essay is about whales. Remind them that knowing the topic, however, doesn't mean they know the main idea.
Instruct the students to examine the first paragraph of the essay. Explain that this is usually an introduction to the entire essay and contains the main idea. The main idea, which is the basic concept of the essay, can frequently be found at the beginning or end of the first paragraph. Often the main idea is stated explicitly in a sentence or two, which is called the thesis statement, but it may occasionally not be stated directly. Since they know from skimming the essay that the general idea is about whales, have them review the first paragraph to see if it makes a statement about whales. If they find a statement that seems to be the main idea, have them check the remaining paragraphs. These should relate to the point about whales the author is making and supporting.
Tell your students that in this example the author wants to correct the mistaken idea that whales are fish because they live in water and have fish-like shapes. Thus, the author's main idea is that whales are mammals. Help them discover that each paragraph offers evidence to prove the author's statement, such as whales give birth to live young, breathe air with lungs by getting their nostrils above the water and maintain a level body temperature in spite of temperature changes to their environment. If the main idea is not stated directly, instruct the students to look for clues in each of the paragraphs. Putting the ideas from the paragraphs together should lead them to the main idea.
Determine the main idea of each paragraph by having the students examine each paragraph. Explain that authors usually make the first or last sentence of a paragraph the statement of the paragraph's main idea. The paragraphs' main ideas will be the supporting ideas of the essay's main idea.