Type a paragraph from your class's social studies textbook on a sheet of acetate and project it with the overhead projector.

Have a child read the selection aloud and involve the class in a discussion of the main idea.

Ask which words from the selection can be omitted from the passage without losing or distorting the author's message.

As children decide which words are unnecessary, cross them out with an erasable marker.

Have the students reread the passage several times during this procedure to make sure that the kernel of the paragraph is still intact.
Erase your cross-out marks and read the original paragraph again.
Invite a child to state the main idea in his or her own words.

As a follow-up, distribute copies with two or three other paragraphs from the same textbook.
Instruct the children to independently cross out the unnecessary words and then state the main idea in as few words as possible. When they become reasonably skilled at isolating main ideas, reverse the process by having them build a paragraph around a thought expressed in a single sentence