How do you write an argumentative essay over " the school board of your district is considering making the school day longer by adding an extra hour. the purpose for lengthening the school day is to provide more time for learning

First, use some facts/opinions to explain why you disagree with this. For Example: "The school day should not be lengthened by an hour because it restricts social development with friends and family, and would actually cause more stress on students. Many students are involved in outside activities, and this will cause many problems." (You can use these if you wish by the way! Just be sure to reword it)
Then try to have some back-up evidence (if you can)
Write ONE paragraph about some POSITIVES about adding an extra hour
Write a short conclusion, going over the strong points you had talked about, but do NOT repeat exactly what you said. 
Hope this helps!