Agree with stealth. However; if you want a "Constructive" (OPINION); here's mine.
When writing an essay, paper, report, etc... there are only 3 real options for spacing. 1) Single space; 2) Double space; 3) 1 1/2 space.
When READING, the majority of all print in a book, magazine, online, is done in Single Space.
Therefor, if someone like the MOC instructed me to do a "1 page" essay, I would error on the side of the person "Reading it". Meaning; being the person is going to be reading the essay, they are accustomed to reading the majority of all things in "Single Space". Therefor, I would write the essay; no longer than 1 page; in "Single Space". It shows that you didn't assume the "Easiest" way out. (Less words/shorter essay). You followed the instructions of No More than 1 page.
The instructions didn't say to only use 1-2 syllable words; so you're using your NORMAL vocabulary. Well; the instructions didn't say single, double, or 1.5 spacing, so use the NORMAL SPACING. And "NORMAL" spacing for READING; which is what the MOC/Staff will be doing; is "Single Space". NORMAL reading isn't double or 1.5 spaced.
In other words; based on the instructions; you COULD be dinged for double spacing as a means of providing a "Easier" essay. But you can't be dinged for a single spaced essay because the instructions didn't say otherwise and you erred on the side of cautiousness. Just like you would budget for worse case scenario, you should write based on most extensive required essay.
Just my opinion. Mike....