The five-paragraph essay is a form of convergent thought. It encourages the writer to fit information into a formula: an introduction stating a main idea and sometimes naming three supporting points; three body paragraphs, one for each point; and a conclusion renaming the main idea and three points.
For example, a student writer might choose for an essay topic an uncontroversial idea, such as that smoking is bad for health. The writer might choose as the three points 1) smoking destroys lungs, 2) smoking leads to diseases like lung cancer, and 3) smoking leads to facial wrinkles. But what if the writer thinks, wait a minute, wrinkles aren’t a health problem. The writer ponders, searching for a third reason why smoking is bad for health, and can’t think of one. So the writer changes his topic completely to fit the five-paragraph format.
What if the writer had instead researched wrinkles to see if there is any connection to smoking and health? The writer might have learned that wrinkles are a health concern. He might have learned about research connecting wrinkles and smoking and health. He might have learned some open-ended questions which scientists are striving to answer. He might have learned.
The problem with the five-paragraph essay is that it encourages closed-minded thinking, not learning. It encourages simplistic, not complex, thinking. It encourages safety, not exploration of ideas. It encourages fill-in-the-blanks, not critical thinking.