TOEFL iBT Integrated Writing Structure.
The basic structure of a integrated writing essay should look like this -

Introductory paragraph
In this set of materials, the reading passage  __(main idea of reading passage)_____, and the listening passage (main idea of listening passage + connection between passages)___ .
Paragraph describing Reading passage
The reading passage __(main idea of reading passage restated)___ .
Main point 1
Supporting details
Main point 2
Supporting details
Main point 3
Supporting details
(The number of main points will depend on the information in the two passages. There is NO standard number.)
Paragraph describing Listening passage
The listening passage __(main idea of listening passage restated)___ .
Main point 1
Supporting details
Main point 2
Supporting details
(How many supporting details you can include depends on time and importance of the details. You DO NOT have to include all supporting details.)
Concluding paragraph or sentence is not necessary
 
Lets look at a sample set of materials
Click here to review the 'Library at Alexandria' reading and listening materials, and sample notes

Introductory paragraph

In this set of materials, the reading passage describes the ancient library at Alexandria, and the listening passage discusses how and when it was destroyed.
Body Paragraph 1 describing Reading passage

The reading passage informs us that the library at Alexandria was the greatest in the ancient world, with the largest collection of books existing at that time. It was founded by Ptolemy I and greatly expanded under Ptolemy II. Ptolemy wished to gather not only a copy of every book ever written in Greek, but also works from other countries. As a result the library was said to contain hundreds of thousands of books. The books were acquired in various ways. Some were bought, some were obtained through trade, some taken from citizens in debt to the state, and others from ships in Alexandria harbour.
Body Paragraph 2 describing Listening passage

In the listening passage, we are told that the library no longer exists and that there is debate about its fate. Traditionally, Julius Caesar was blamed for the destruction of the library. He attacked Alexandria in 48 BCE and it was thought the library was burned down during the assault. However, scholars now feel that this was not so. The library was mentioned in works written hundreds of years after Caesar’s death, and these references continued up to the 4th century CE. It seems that around this time the people of Alexandria started to destroy non-Christian temples and books, and it is considered likely that the library was destroyed at this time. (241)
Concluding paragraph or sentence is not necessary

Important Points
1) The words used to introduce the main ideas should be different each time.
Look at the introduction. The writer uses the word 'describes' to introduce the main idea of the reading passage.
What words are used to introduce the main idea of the listening passage?
What words are used to introduce the main ideas in the the two body paragraphs?
2) You should try to use synonyms whenever you can.
Look at the word 'greatly' in the middle of body paragraph 1. It is a synonym for 'tremendously'
Can you see any other synonyms?
3) You need linking words to hold your essay together.
Look at the words 'As aresult' in body paragraph 1. They tell the reader that things are connected, or that you are moving on to another point.
Can you see any other linking words?


A note about conclusions
Please do not write a conclusion in the real test, you will not have time to do this.
However, if I had to write a conclusion, perhaps in a non-TOEFL test academic essay, I might write something like this -
Again we can see evidence that the study of history is not a rigid discipline and that accepted ‘truths’ are often challenged in later years.