This is an interesting topic; however, I am not allowed to write the descriptive essay for you. I can offer some suggestions and guidance, and that will hopefully set the essay in the desired direction.
1,000 words isn't that terrible huge of a number, but it does give you plenty of writing space in which to craft a fairly detailed essay. From the Enotes post, it looks like the 1,000 word is the maximum limit. If that is the case, don't go over the limit. Teachers set those limits intentionally for their own grading time constraints. Teachers also set upper limits because they want to see if a student can get his/her point across in a set amount of time.
Before even beginning to write the essay, you need to decide on some key writing elements. One thing that you need to decide is regarding your audience. Who is your audience? It could be your teacher, but it doesn't have to be. You could decide that your audience is your younger sibling or a peer of yours. Knowing your audience is important because it guides things like word choice.
A second thing to decide is point of view. What will be the narrator's point of view? First person uses "I" and "we." Using this point of view might be an accessible writing route because you can speak from your own point of view and personal emotions. Of course, the first person point of view doesn't need to be you. You could decide to have your first person narrator be a hypothetical student. It could be the class clown. It could be the school's resident jock, or it could be the class president. Each of those people are likely to respond differently to a classroom without a teacher. You could even go in a completely different direction and write a first person account from the perspective of the classroom pet. This is how the Humphrey book series is written. Humphrey is the class's pet hamster. You could even choose to write a first person account from the perspective of an classroom object like the whiteboard.
The point of view could be third person. This will use "he," "she," and "they." It's an effective narrative point of view because it allows the narrator to have access to everybody's thoughts, emotions, and actions. Finally, the essay could be written in second person. This point of view uses "you"—"you walk into the classroom late only to find that the teacher is gone." Second person narration is rarely used, but it could be a super cool perspective for this essay because it puts your reader as the one experiencing everything.
Once you have the audience and narrative point of view figured out, I recommend brainstorming about five different categories. The essay is a descriptive essay. It needs to describe things in detail. A plot that has conflict and resolution isn't the focus. The descriptive experience is the focus. Brainstorm about the experiences of all five senses in that classroom with no teacher. What does it sound like? What does it look like? Are there smells or tastes that are different from normal? Once you have a general idea of what experiences the narrator is going to describe, it's time to "jazz up" the descriptions. Use lots of adjectives, and make the adjectives specific. "Big," "good," and "beautiful" are too vague. Use similes and metaphors to make comparisons for your readers. Go for things like personification and even onomatopoeia.
If your essay is going to focus on the five senses, organize those by paragraph. People don't experience things this way in real life. We take in sights and smells all at once, but if you write it out as a stream of consciousness piece, you run the risk of confusing your reader. Move from sense to sense by paragraph, and the reader experiences a much more organized descriptive essay.