Great, I want to know that too! Look what I downloaded from an ETS website:
Paragraph One: The first sentence in the first paragraph is the “hook,” whose purpose is to catch the reader’s attention and make him or her WANT to read your essay. The next several sentences of the first paragraph serve to explain the background, history, etc… of the topic, but WITHOUT giving away the writer’s own point of view. This is kind of like a card game, in which letting the other players know how excited you are about the hand you’ve been dealt can greatly diminish the value of that hand. The last sentence of the first paragraph is the antithesis-thesis, or opinion, statement. This is inserted verbatim from Step 6 of the pre-writing process, and serves as a map for the rest of the essay.
Paragraph Two: The first sentence in paragraph two presents the main reason given by those who believe the opposing opinion. The rest of the paragraph explains and then breaks down, or disproves,this reasoning through the use of examples, evidence, experience and logical argument. The goal is to weaken the opposing argument enough that the reader is inclined to set it aside and open his or her mind to the writer’s own argument.
Paragraph Three: The first sentence in paragraph three gives the first of two reasons in favor of the writer’s opinion, also restating that opinion to help the reader follow the argument as carefully as possible. The rest of the paragraph is a proof of this first reason, using supporting examples, evide-nce and personal experience to form a logical argument that persuades the reader to accept the reasoning.
Paragraph Four: This paragraph presents and proves the second reason in favor of the writer’s thesis. Also, because the TOEFL is a timed exercise, an enthusiastic concluding sentence is tagged onto the end of this final paragraph, converting the paragraph into a conclusion.