It's not fair to assume that's what this teacher asks of their students. Word minimums may be useful for children as a crude deterrent against laziness, but any serious student or teacher would recognize a good essay when they see one, no matter the length (though fitting a good and interesting essay on the back of a napkin would be almost unthinkably prolific).

"I have made this letter longer than usual, only because I have not had the time to make it shorter." - Blaise Pascal